1 | (* *********************************************************************) |
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2 | (* *) |
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3 | (* The Compcert verified compiler *) |
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4 | (* *) |
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5 | (* Xavier Leroy, INRIA Paris-Rocquencourt *) |
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6 | (* *) |
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7 | (* Copyright Institut National de Recherche en Informatique et en *) |
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8 | (* Automatique. All rights reserved. This file is distributed *) |
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9 | (* under the terms of the GNU General Public License as published by *) |
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10 | (* the Free Software Foundation, either version 2 of the License, or *) |
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11 | (* (at your option) any later version. This file is also distributed *) |
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12 | (* under the terms of the INRIA Non-Commercial License Agreement. *) |
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13 | (* *) |
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14 | (* *********************************************************************) |
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15 | |
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16 | (* Formalizations of machine integers modulo $2^N$ #2<sup>N</sup>#. *) |
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17 | |
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18 | include "arithmetics/nat.ma". |
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19 | include "binary/Z.ma". |
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20 | include "extralib.ma". |
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21 | |
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22 | |
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23 | (* * * Comparisons *) |
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24 | |
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25 | inductive comparison : Type[0] ≝ |
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26 | | Ceq : comparison (**r same *) |
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27 | | Cne : comparison (**r different *) |
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28 | | Clt : comparison (**r less than *) |
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29 | | Cle : comparison (**r less than or equal *) |
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30 | | Cgt : comparison (**r greater than *) |
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31 | | Cge : comparison. (**r greater than or equal *) |
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32 | |
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33 | definition negate_comparison : comparison → comparison ≝ λc. |
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34 | match c with |
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35 | [ Ceq ⇒ Cne |
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36 | | Cne ⇒ Ceq |
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37 | | Clt ⇒ Cge |
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38 | | Cle ⇒ Cgt |
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39 | | Cgt ⇒ Cle |
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40 | | Cge ⇒ Clt |
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41 | ]. |
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42 | |
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43 | definition swap_comparison : comparison → comparison ≝ λc. |
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44 | match c with |
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45 | [ Ceq ⇒ Ceq |
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46 | | Cne ⇒ Cne |
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47 | | Clt ⇒ Cgt |
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48 | | Cle ⇒ Cge |
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49 | | Cgt ⇒ Clt |
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50 | | Cge ⇒ Cle |
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51 | ]. |
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52 | (* |
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53 | (** * Parameterization by the word size, in bits. *) |
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54 | |
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55 | Module Type WORDSIZE. |
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56 | Variable wordsize: nat. |
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57 | Axiom wordsize_not_zero: wordsize <> 0%nat. |
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58 | End WORDSIZE. |
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59 | |
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60 | Module Make(WS: WORDSIZE). |
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61 | |
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62 | *) |
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63 | |
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64 | (*axiom two_power_nat : nat → Z.*) |
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65 | |
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66 | definition wordsize : nat ≝ 32. |
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67 | definition modulus : Z ≝ Z_two_power_nat wordsize. |
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68 | definition half_modulus : Z ≝ modulus / 2. |
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69 | definition max_unsigned : Z ≝ modulus - 1. |
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70 | definition max_signed : Z ≝ half_modulus - 1. |
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71 | definition min_signed : Z ≝ - half_modulus. |
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72 | |
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73 | lemma wordsize_pos: |
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74 | Z_of_nat wordsize > 0. |
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75 | normalize; //; qed. |
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76 | |
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77 | lemma modulus_power: |
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78 | modulus = two_p (Z_of_nat wordsize). |
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79 | //; qed. |
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80 | |
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81 | lemma modulus_pos: |
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82 | modulus > 0. |
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83 | //; qed. |
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84 | |
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85 | (* * Representation of machine integers *) |
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86 | |
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87 | (* A machine integer (type [int]) is represented as a Coq arbitrary-precision |
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88 | integer (type [Z]) plus a proof that it is in the range 0 (included) to |
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89 | [modulus] (excluded. *) |
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90 | (* XXX: hack to prevent normalization of huge proof term. *) |
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91 | inductive inrange : Z → Prop ≝ |
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92 | | inrg_mod : ∀i:Z. inrange (i \mod modulus) |
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93 | | inrg_pf : ∀i:Z. (0 ≤ i) ∧ i < modulus → inrange i. |
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94 | inductive int: Type[0] ≝ |
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95 | | mk_int: ∀i:Z. inrange i → int. |
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96 | (* |
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97 | record int: Type ≝ { intval: Z ; intrange: (0 ≤ intval) ∧ intval < modulus }. |
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98 | *) |
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99 | definition intval: int → Z ≝ λi.match i with [ mk_int x _ ⇒ x ]. |
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100 | definition intrange: ∀i:int. 0 ≤ (intval i) ∧ (intval i) < modulus. |
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101 | #i cases i; |
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102 | #x #H cases H; |
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103 | [ #x' @modZ_lt_mod //; |
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104 | | //; |
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105 | ] qed. |
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106 | |
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107 | (* The [unsigned] and [signed] functions return the Coq integer corresponding |
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108 | to the given machine integer, interpreted as unsigned or signed |
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109 | respectively. *) |
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110 | |
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111 | definition unsigned : int → Z ≝ intval. |
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112 | |
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113 | definition signed : int → Z ≝ λn. |
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114 | if Zltb (unsigned n) half_modulus |
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115 | then unsigned n |
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116 | else unsigned n - modulus. |
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117 | |
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118 | (* Conversely, [repr] takes a Coq integer and returns the corresponding |
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119 | machine integer. The argument is treated modulo [modulus]. *) |
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120 | (*axiom repr : Z → int.*) |
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121 | (* |
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122 | definition repr : Z → int := λx. |
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123 | mk_int (x \mod modulus) (modZ_lt_mod x modulus modulus_pos). |
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124 | *) |
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125 | definition repr : Z → int ≝ λx. mk_int (x \mod modulus) (inrg_mod x). |
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126 | |
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127 | definition zero := repr 0. |
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128 | definition one := repr 1. |
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129 | definition mone := repr (-1). |
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130 | definition iwordsize := repr (Z_of_nat wordsize). |
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131 | |
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132 | axiom mk_int_eq: |
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133 | ∀x,y,Px,Py. x = y → mk_int x Px = mk_int y Py. |
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134 | (*Proof. |
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135 | intros. subst y. |
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136 | generalize (proof_irrelevance _ Px Py); intro. |
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137 | subst Py. reflexivity. |
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138 | Qed.*) |
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139 | |
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140 | axiom eq_dec: ∀x,y: int. (x = y) + (x ≠ y). |
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141 | (*Proof. |
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142 | intros. destruct x; destruct y. case (zeq intval0 intval1); intro. |
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143 | left. apply mkint_eq. auto. |
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144 | right. red; intro. injection H. exact n. |
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145 | Qed.*) |
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146 | |
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147 | (* * Arithmetic and logical operations over machine integers *) |
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148 | |
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149 | definition eq : int → int → bool ≝ λx,y: int. |
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150 | if eqZb (unsigned x) (unsigned y) then true else false. |
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151 | definition lt : int → int → bool ≝ λx,y:int. |
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152 | if Zltb (signed x) (signed y) then true else false. |
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153 | definition ltu : int → int → bool ≝ λx,y: int. |
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154 | if Zltb (unsigned x) (unsigned y) then true else false. |
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155 | |
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156 | definition neg : int → int ≝ λx. repr (- unsigned x). |
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157 | |
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158 | let rec zero_ext (n:Z) (x:int) on x : int ≝ |
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159 | repr (modZ (unsigned x) (two_p n)). |
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160 | let rec sign_ext (n:Z) (x:int) on x : int ≝ |
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161 | repr (let p ≝ two_p n in |
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162 | let y ≝ modZ (unsigned x) p in |
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163 | if Zltb y (two_p (n-1)) then y else y - p). |
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164 | |
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165 | definition add ≝ λx,y: int. |
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166 | repr (unsigned x + unsigned y). |
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167 | definition sub ≝ λx,y: int. |
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168 | repr (unsigned x - unsigned y). |
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169 | definition mul ≝ λx,y: int. |
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170 | repr (unsigned x * unsigned y). |
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171 | definition Zdiv_round : Z → Z → Z ≝ λx,y: Z. |
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172 | if Zltb x 0 then |
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173 | if Zltb y 0 then (-x) / (-y) else - ((-x) / y) |
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174 | else |
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175 | if Zltb y 0 then -(x / (-y)) else x / y. |
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176 | |
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177 | definition Zmod_round : Z → Z → Z ≝ λx,y: Z. |
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178 | x - (Zdiv_round x y) * y. |
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179 | |
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180 | definition divs : int → int → int ≝ λx,y:int. |
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181 | repr (Zdiv_round (signed x) (signed y)). |
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182 | definition mods : int → int → int ≝ λx,y:int. |
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183 | repr (Zmod_round (signed x) (signed y)). |
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184 | definition divu : int → int → int ≝ λx,y. |
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185 | repr (unsigned x / unsigned y). |
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186 | definition modu : int → int → int ≝ λx,y. |
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187 | repr (unsigned x \mod unsigned y). |
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188 | |
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189 | (* * For bitwise operations, we need to convert between Coq integers [Z] |
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190 | and their bit-level representations. Bit-level representations are |
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191 | represented as characteristic functions, that is, functions [f] |
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192 | of type [nat -> bool] such that [f i] is the value of the [i]-th bit |
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193 | of the number. The values of characteristic functions for [i] greater |
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194 | than 32 are ignored. *) |
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195 | |
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196 | definition Z_shift_add ≝ λb: bool. λx: Z. |
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197 | if b then 2 * x + 1 else 2 * x. |
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198 | |
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199 | definition Z_bin_decomp : Z → bool × Z ≝ |
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200 | λx.match x with |
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201 | [ OZ ⇒ 〈false, OZ〉 |
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202 | | pos p ⇒ |
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203 | match p with |
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204 | [ p1 q ⇒ 〈true, pos q〉 |
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205 | | p0 q ⇒ 〈false, pos q〉 |
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206 | | one ⇒ 〈true, OZ〉 |
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207 | ] |
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208 | | neg p ⇒ |
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209 | match p with |
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210 | [ p1 q ⇒ 〈true, Zpred (neg q)〉 |
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211 | | p0 q ⇒ 〈false, neg q〉 |
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212 | | one ⇒ 〈true, neg one〉 |
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213 | ] |
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214 | ]. |
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215 | |
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216 | let rec bits_of_Z (n:nat) (x:Z) on n : Z → bool ≝ |
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217 | match n with |
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218 | [ O ⇒ λi:Z. false |
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219 | | S m ⇒ |
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220 | match Z_bin_decomp x with [ pair b y ⇒ |
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221 | let f ≝ bits_of_Z m y in |
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222 | λi:Z. if eqZb i 0 then b else f (Zpred i) ] |
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223 | ]. |
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224 | |
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225 | let rec Z_of_bits (n:nat) (f:Z → bool) on n : Z ≝ |
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226 | match n with |
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227 | [ O ⇒ OZ |
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228 | | S m ⇒ Z_shift_add (f OZ) (Z_of_bits m (λi. f (Zsucc i))) |
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229 | ]. |
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230 | |
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231 | (* * Bitwise logical ``and'', ``or'' and ``xor'' operations. *) |
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232 | |
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233 | definition bitwise_binop ≝ λf: bool -> bool -> bool. λx,y: int. |
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234 | let fx ≝ bits_of_Z wordsize (unsigned x) in |
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235 | let fy ≝ bits_of_Z wordsize (unsigned y) in |
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236 | repr (Z_of_bits wordsize (λi. f (fx i) (fy i))). |
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237 | |
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238 | definition i_and : int → int → int ≝ λx,y. bitwise_binop andb x y. |
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239 | definition or : int → int → int ≝ λx,y. bitwise_binop orb x y. |
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240 | definition xor : int → int → int ≝ λx,y. bitwise_binop xorb x y. |
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241 | |
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242 | definition not : int → int ≝ λx.xor x mone. |
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243 | |
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244 | (* * Shifts and rotates. *) |
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245 | |
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246 | definition shl : int → int → int ≝ λx,y. |
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247 | let fx ≝ bits_of_Z wordsize (unsigned x) in |
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248 | let vy ≝ unsigned y in |
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249 | repr (Z_of_bits wordsize (λi. fx (i - vy))). |
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250 | |
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251 | definition shru : int → int → int ≝ λx,y. |
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252 | let fx ≝ bits_of_Z wordsize (unsigned x) in |
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253 | let vy ≝ unsigned y in |
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254 | repr (Z_of_bits wordsize (λi. fx (i + vy))). |
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255 | |
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256 | (* * Arithmetic right shift is defined as signed division by a power of two. |
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257 | Two such shifts are defined: [shr] rounds towards minus infinity |
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258 | (standard behaviour for arithmetic right shift) and |
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259 | [shrx] rounds towards zero. *) |
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260 | |
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261 | definition shr : int → int → int ≝ λx,y. |
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262 | repr (signed x / two_p (unsigned y)). |
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263 | |
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264 | definition shrx : int → int → int ≝ λx,y. |
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265 | divs x (shl one y). |
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266 | |
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267 | definition shr_carry ≝ λx,y: int. |
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268 | sub (shrx x y) (shr x y). |
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269 | |
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270 | definition rol : int → int → int ≝ λx,y. |
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271 | let fx ≝ bits_of_Z wordsize (unsigned x) in |
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272 | let vy ≝ unsigned y in |
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273 | repr (Z_of_bits wordsize |
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274 | (λi. fx (i - vy \mod Z_of_nat wordsize))). |
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275 | |
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276 | definition ror : int → int → int ≝ λx,y. |
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277 | let fx := bits_of_Z wordsize (unsigned x) in |
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278 | let vy := unsigned y in |
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279 | repr (Z_of_bits wordsize |
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280 | (λi. fx (i + vy \mod Z_of_nat wordsize))). |
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281 | |
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282 | definition rolm ≝ λx,a,m: int. i_and (rol x a) m. |
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283 | (* |
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284 | (** Decomposition of a number as a sum of powers of two. *) |
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285 | |
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286 | Fixpoint Z_one_bits (n: nat) (x: Z) (i: Z) {struct n}: list Z := |
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287 | match n with |
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288 | | O => nil |
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289 | | S m => |
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290 | let (b, y) := Z_bin_decomp x in |
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291 | if b then i :: Z_one_bits m y (i+1) else Z_one_bits m y (i+1) |
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292 | end. |
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293 | |
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294 | Definition one_bits (x: int) : list int := |
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295 | List.map repr (Z_one_bits wordsize (unsigned x) 0). |
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296 | |
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297 | (** Recognition of powers of two. *) |
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298 | |
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299 | Definition is_power2 (x: int) : option int := |
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300 | match Z_one_bits wordsize (unsigned x) 0 with |
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301 | | i :: nil => Some (repr i) |
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302 | | _ => None |
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303 | end. |
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304 | |
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305 | (** Recognition of integers that are acceptable as immediate operands |
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306 | to the [rlwim] PowerPC instruction. These integers are of the form |
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307 | [000011110000] or [111100001111], that is, a run of one bits |
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308 | surrounded by zero bits, or conversely. We recognize these integers by |
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309 | running the following automaton on the bits. The accepting states are |
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310 | 2, 3, 4, 5, and 6. |
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311 | << |
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312 | 0 1 0 |
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313 | / \ / \ / \ |
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314 | \ / \ / \ / |
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315 | -0--> [1] --1--> [2] --0--> [3] |
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316 | / |
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317 | [0] |
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318 | \ |
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319 | -1--> [4] --0--> [5] --1--> [6] |
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320 | / \ / \ / \ |
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321 | \ / \ / \ / |
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322 | 1 0 1 |
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323 | >> |
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324 | *) |
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325 | |
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326 | Inductive rlw_state: Type := |
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327 | | RLW_S0 : rlw_state |
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328 | | RLW_S1 : rlw_state |
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329 | | RLW_S2 : rlw_state |
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330 | | RLW_S3 : rlw_state |
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331 | | RLW_S4 : rlw_state |
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332 | | RLW_S5 : rlw_state |
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333 | | RLW_S6 : rlw_state |
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334 | | RLW_Sbad : rlw_state. |
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335 | |
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336 | Definition rlw_transition (s: rlw_state) (b: bool) : rlw_state := |
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337 | match s, b with |
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338 | | RLW_S0, false => RLW_S1 |
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339 | | RLW_S0, true => RLW_S4 |
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340 | | RLW_S1, false => RLW_S1 |
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341 | | RLW_S1, true => RLW_S2 |
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342 | | RLW_S2, false => RLW_S3 |
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343 | | RLW_S2, true => RLW_S2 |
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344 | | RLW_S3, false => RLW_S3 |
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345 | | RLW_S3, true => RLW_Sbad |
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346 | | RLW_S4, false => RLW_S5 |
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347 | | RLW_S4, true => RLW_S4 |
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348 | | RLW_S5, false => RLW_S5 |
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349 | | RLW_S5, true => RLW_S6 |
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350 | | RLW_S6, false => RLW_Sbad |
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351 | | RLW_S6, true => RLW_S6 |
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352 | | RLW_Sbad, _ => RLW_Sbad |
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353 | end. |
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354 | |
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355 | Definition rlw_accepting (s: rlw_state) : bool := |
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356 | match s with |
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357 | | RLW_S0 => false |
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358 | | RLW_S1 => false |
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359 | | RLW_S2 => true |
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360 | | RLW_S3 => true |
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361 | | RLW_S4 => true |
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362 | | RLW_S5 => true |
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363 | | RLW_S6 => true |
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364 | | RLW_Sbad => false |
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365 | end. |
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366 | |
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367 | Fixpoint is_rlw_mask_rec (n: nat) (s: rlw_state) (x: Z) {struct n} : bool := |
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368 | match n with |
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369 | | O => |
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370 | rlw_accepting s |
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371 | | S m => |
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372 | let (b, y) := Z_bin_decomp x in |
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373 | is_rlw_mask_rec m (rlw_transition s b) y |
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374 | end. |
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375 | |
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376 | Definition is_rlw_mask (x: int) : bool := |
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377 | is_rlw_mask_rec wordsize RLW_S0 (unsigned x). |
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378 | *) |
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379 | (* * Comparisons. *) |
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380 | |
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381 | definition cmp : comparison → int → int → bool ≝ λc,x,y. |
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382 | match c with |
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383 | [ Ceq ⇒ eq x y |
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384 | | Cne ⇒ notb (eq x y) |
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385 | | Clt ⇒ lt x y |
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386 | | Cle ⇒ notb (lt y x) |
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387 | | Cgt ⇒ lt y x |
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388 | | Cge ⇒ notb (lt x y) |
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389 | ]. |
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390 | |
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391 | definition cmpu : comparison → int → int → bool ≝ λc,x,y. |
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392 | match c with |
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393 | [ Ceq ⇒ eq x y |
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394 | | Cne ⇒ notb (eq x y) |
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395 | | Clt ⇒ ltu x y |
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396 | | Cle ⇒ notb (ltu y x) |
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397 | | Cgt ⇒ ltu y x |
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398 | | Cge ⇒ notb (ltu x y) |
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399 | ]. |
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400 | |
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401 | definition is_false : int → Prop ≝ λx. x = zero. |
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402 | definition is_true : int → Prop ≝ λx. x ≠ zero. |
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403 | definition notbool : int → int ≝ λx. if eq x zero then one else zero. |
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404 | (* |
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405 | (** * Properties of integers and integer arithmetic *) |
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406 | |
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407 | (** ** Properties of [modulus], [max_unsigned], etc. *) |
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408 | |
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409 | Remark half_modulus_power: |
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410 | half_modulus = two_p (Z_of_nat wordsize - 1). |
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411 | Proof. |
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412 | unfold half_modulus. rewrite modulus_power. |
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413 | set (ws1 := Z_of_nat wordsize - 1). |
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414 | replace (Z_of_nat wordsize) with (Zsucc ws1). |
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415 | rewrite two_p_S. rewrite Zmult_comm. apply Z_div_mult. omega. |
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416 | unfold ws1. generalize wordsize_pos; omega. |
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417 | unfold ws1. omega. |
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418 | Qed. |
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419 | |
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420 | Remark half_modulus_modulus: modulus = 2 * half_modulus. |
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421 | Proof. |
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422 | rewrite half_modulus_power. rewrite modulus_power. |
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423 | rewrite <- two_p_S. decEq. omega. |
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424 | generalize wordsize_pos; omega. |
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425 | Qed. |
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426 | |
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427 | (** Relative positions, from greatest to smallest: |
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428 | << |
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429 | max_unsigned |
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430 | max_signed |
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431 | 2*wordsize-1 |
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432 | wordsize |
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433 | 0 |
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434 | min_signed |
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435 | >> |
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436 | *) |
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437 | |
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438 | Remark half_modulus_pos: half_modulus > 0. |
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439 | Proof. |
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440 | rewrite half_modulus_power. apply two_p_gt_ZERO. generalize wordsize_pos; omega. |
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441 | Qed. |
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442 | |
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443 | Remark min_signed_neg: min_signed < 0. |
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444 | Proof. |
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445 | unfold min_signed. generalize half_modulus_pos. omega. |
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446 | Qed. |
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447 | |
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448 | Remark max_signed_pos: max_signed >= 0. |
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449 | Proof. |
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450 | unfold max_signed. generalize half_modulus_pos. omega. |
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451 | Qed. |
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452 | |
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453 | Remark wordsize_max_unsigned: Z_of_nat wordsize <= max_unsigned. |
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454 | Proof. |
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455 | assert (Z_of_nat wordsize < modulus). |
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456 | rewrite modulus_power. apply two_p_strict. |
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457 | generalize wordsize_pos. omega. |
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458 | unfold max_unsigned. omega. |
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459 | Qed. |
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460 | |
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461 | Remark two_wordsize_max_unsigned: 2 * Z_of_nat wordsize - 1 <= max_unsigned. |
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462 | Proof. |
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463 | assert (2 * Z_of_nat wordsize - 1 < modulus). |
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464 | rewrite modulus_power. apply two_p_strict_2. generalize wordsize_pos; omega. |
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465 | unfold max_unsigned; omega. |
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466 | Qed. |
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467 | |
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468 | Remark max_signed_unsigned: max_signed < max_unsigned. |
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469 | Proof. |
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470 | unfold max_signed, max_unsigned. rewrite half_modulus_modulus. |
---|
471 | generalize half_modulus_pos. omega. |
---|
472 | Qed. |
---|
473 | |
---|
474 | (** ** Properties of zero, one, minus one *) |
---|
475 | |
---|
476 | Theorem unsigned_zero: unsigned zero = 0. |
---|
477 | Proof. |
---|
478 | simpl. apply Zmod_0_l. |
---|
479 | Qed. |
---|
480 | |
---|
481 | Theorem unsigned_one: unsigned one = 1. |
---|
482 | Proof. |
---|
483 | simpl. apply Zmod_small. split. omega. |
---|
484 | unfold modulus. replace wordsize with (S(pred wordsize)). |
---|
485 | rewrite two_power_nat_S. generalize (two_power_nat_pos (pred wordsize)). |
---|
486 | omega. |
---|
487 | generalize wordsize_pos. omega. |
---|
488 | Qed. |
---|
489 | |
---|
490 | Theorem unsigned_mone: unsigned mone = modulus - 1. |
---|
491 | Proof. |
---|
492 | simpl unsigned. |
---|
493 | replace (-1) with ((modulus - 1) + (-1) * modulus). |
---|
494 | rewrite Z_mod_plus_full. apply Zmod_small. |
---|
495 | generalize modulus_pos. omega. omega. |
---|
496 | Qed. |
---|
497 | |
---|
498 | Theorem signed_zero: signed zero = 0. |
---|
499 | Proof. |
---|
500 | unfold signed. rewrite unsigned_zero. apply zlt_true. generalize half_modulus_pos; omega. |
---|
501 | Qed. |
---|
502 | |
---|
503 | Theorem signed_mone: signed mone = -1. |
---|
504 | Proof. |
---|
505 | unfold signed. rewrite unsigned_mone. |
---|
506 | rewrite zlt_false. omega. |
---|
507 | rewrite half_modulus_modulus. generalize half_modulus_pos. omega. |
---|
508 | Qed. |
---|
509 | *) |
---|
510 | axiom one_not_zero: one ≠ zero. |
---|
511 | (* |
---|
512 | Theorem one_not_zero: one <> zero. |
---|
513 | Proof. |
---|
514 | assert (unsigned one <> unsigned zero). |
---|
515 | rewrite unsigned_one; rewrite unsigned_zero; congruence. |
---|
516 | congruence. |
---|
517 | Qed. |
---|
518 | |
---|
519 | Theorem unsigned_repr_wordsize: |
---|
520 | unsigned iwordsize = Z_of_nat wordsize. |
---|
521 | Proof. |
---|
522 | simpl. apply Zmod_small. |
---|
523 | generalize wordsize_pos wordsize_max_unsigned; unfold max_unsigned; omega. |
---|
524 | Qed. |
---|
525 | *) |
---|
526 | (* * ** Properties of equality *) |
---|
527 | |
---|
528 | theorem eq_sym: |
---|
529 | ∀x,y. eq x y = eq y x. |
---|
530 | #x #y whd in ⊢ (??%%); @eqZb_elim #H |
---|
531 | [ >H >(eqZb_z_z …) // |
---|
532 | | >(eqZb_false … (sym_neq … H)) // |
---|
533 | ] qed. |
---|
534 | |
---|
535 | theorem eq_spec: ∀x,y: int. if eq x y then x = y else (x ≠ y). |
---|
536 | #x #y whd in ⊢ (??%??); elim (eq_dec x y); #H |
---|
537 | [ >H >(eqZb_z_z …) //; |
---|
538 | | >(eqZb_false …) //; |
---|
539 | elim x in H ⊢ %; elim y; |
---|
540 | #x' #Px #y' #Py #H normalize; @(not_to_not … H) @mk_int_eq |
---|
541 | ] qed. |
---|
542 | |
---|
543 | theorem eq_true: ∀x. eq x x = true. |
---|
544 | #x lapply (eq_spec x x); elim (eq x x); //; |
---|
545 | #H normalize in H; @False_ind @(absurd ? (refl ??) H) |
---|
546 | qed. |
---|
547 | |
---|
548 | theorem eq_false: ∀x,y. x ≠ y → eq x y = false. |
---|
549 | #x #y lapply (eq_spec x y); elim (eq x y); //; |
---|
550 | #H #H' @False_ind @(absurd ? H H') |
---|
551 | qed. |
---|
552 | (* |
---|
553 | (** ** Modulo arithmetic *) |
---|
554 | |
---|
555 | (** We define and state properties of equality and arithmetic modulo a |
---|
556 | positive integer. *) |
---|
557 | |
---|
558 | Section EQ_MODULO. |
---|
559 | |
---|
560 | Variable modul: Z. |
---|
561 | Hypothesis modul_pos: modul > 0. |
---|
562 | |
---|
563 | Definition eqmod (x y: Z) : Prop := exists k, x = k * modul + y. |
---|
564 | |
---|
565 | Lemma eqmod_refl: forall x, eqmod x x. |
---|
566 | Proof. |
---|
567 | intros; red. exists 0. omega. |
---|
568 | Qed. |
---|
569 | |
---|
570 | Lemma eqmod_refl2: forall x y, x = y -> eqmod x y. |
---|
571 | Proof. |
---|
572 | intros. subst y. apply eqmod_refl. |
---|
573 | Qed. |
---|
574 | |
---|
575 | Lemma eqmod_sym: forall x y, eqmod x y -> eqmod y x. |
---|
576 | Proof. |
---|
577 | intros x y [k EQ]; red. exists (-k). subst x. ring. |
---|
578 | Qed. |
---|
579 | |
---|
580 | Lemma eqmod_trans: forall x y z, eqmod x y -> eqmod y z -> eqmod x z. |
---|
581 | Proof. |
---|
582 | intros x y z [k1 EQ1] [k2 EQ2]; red. |
---|
583 | exists (k1 + k2). subst x; subst y. ring. |
---|
584 | Qed. |
---|
585 | |
---|
586 | Lemma eqmod_small_eq: |
---|
587 | forall x y, eqmod x y -> 0 <= x < modul -> 0 <= y < modul -> x = y. |
---|
588 | Proof. |
---|
589 | intros x y [k EQ] I1 I2. |
---|
590 | generalize (Zdiv_unique _ _ _ _ EQ I2). intro. |
---|
591 | rewrite (Zdiv_small x modul I1) in H. subst k. omega. |
---|
592 | Qed. |
---|
593 | |
---|
594 | Lemma eqmod_mod_eq: |
---|
595 | forall x y, eqmod x y -> x mod modul = y mod modul. |
---|
596 | Proof. |
---|
597 | intros x y [k EQ]. subst x. |
---|
598 | rewrite Zplus_comm. apply Z_mod_plus. auto. |
---|
599 | Qed. |
---|
600 | |
---|
601 | Lemma eqmod_mod: |
---|
602 | forall x, eqmod x (x mod modul). |
---|
603 | Proof. |
---|
604 | intros; red. exists (x / modul). |
---|
605 | rewrite Zmult_comm. apply Z_div_mod_eq. auto. |
---|
606 | Qed. |
---|
607 | |
---|
608 | Lemma eqmod_add: |
---|
609 | forall a b c d, eqmod a b -> eqmod c d -> eqmod (a + c) (b + d). |
---|
610 | Proof. |
---|
611 | intros a b c d [k1 EQ1] [k2 EQ2]; red. |
---|
612 | subst a; subst c. exists (k1 + k2). ring. |
---|
613 | Qed. |
---|
614 | |
---|
615 | Lemma eqmod_neg: |
---|
616 | forall x y, eqmod x y -> eqmod (-x) (-y). |
---|
617 | Proof. |
---|
618 | intros x y [k EQ]; red. exists (-k). rewrite EQ. ring. |
---|
619 | Qed. |
---|
620 | |
---|
621 | Lemma eqmod_sub: |
---|
622 | forall a b c d, eqmod a b -> eqmod c d -> eqmod (a - c) (b - d). |
---|
623 | Proof. |
---|
624 | intros a b c d [k1 EQ1] [k2 EQ2]; red. |
---|
625 | subst a; subst c. exists (k1 - k2). ring. |
---|
626 | Qed. |
---|
627 | |
---|
628 | Lemma eqmod_mult: |
---|
629 | forall a b c d, eqmod a c -> eqmod b d -> eqmod (a * b) (c * d). |
---|
630 | Proof. |
---|
631 | intros a b c d [k1 EQ1] [k2 EQ2]; red. |
---|
632 | subst a; subst b. |
---|
633 | exists (k1 * k2 * modul + c * k2 + k1 * d). |
---|
634 | ring. |
---|
635 | Qed. |
---|
636 | |
---|
637 | End EQ_MODULO. |
---|
638 | |
---|
639 | Lemma eqmod_divides: |
---|
640 | forall n m x y, eqmod n x y -> Zdivide m n -> eqmod m x y. |
---|
641 | Proof. |
---|
642 | intros. destruct H as [k1 EQ1]. destruct H0 as [k2 EQ2]. |
---|
643 | exists (k1*k2). rewrite <- Zmult_assoc. rewrite <- EQ2. auto. |
---|
644 | Qed. |
---|
645 | |
---|
646 | (** We then specialize these definitions to equality modulo |
---|
647 | $2^{wordsize}$ #2<sup>wordsize</sup>#. *) |
---|
648 | |
---|
649 | Hint Resolve modulus_pos: ints. |
---|
650 | |
---|
651 | Definition eqm := eqmod modulus. |
---|
652 | |
---|
653 | Lemma eqm_refl: forall x, eqm x x. |
---|
654 | Proof (eqmod_refl modulus). |
---|
655 | Hint Resolve eqm_refl: ints. |
---|
656 | |
---|
657 | Lemma eqm_refl2: |
---|
658 | forall x y, x = y -> eqm x y. |
---|
659 | Proof (eqmod_refl2 modulus). |
---|
660 | Hint Resolve eqm_refl2: ints. |
---|
661 | |
---|
662 | Lemma eqm_sym: forall x y, eqm x y -> eqm y x. |
---|
663 | Proof (eqmod_sym modulus). |
---|
664 | Hint Resolve eqm_sym: ints. |
---|
665 | |
---|
666 | Lemma eqm_trans: forall x y z, eqm x y -> eqm y z -> eqm x z. |
---|
667 | Proof (eqmod_trans modulus). |
---|
668 | Hint Resolve eqm_trans: ints. |
---|
669 | |
---|
670 | Lemma eqm_samerepr: forall x y, eqm x y -> repr x = repr y. |
---|
671 | Proof. |
---|
672 | intros. unfold repr. apply mkint_eq. |
---|
673 | apply eqmod_mod_eq. auto with ints. exact H. |
---|
674 | Qed. |
---|
675 | |
---|
676 | Lemma eqm_small_eq: |
---|
677 | forall x y, eqm x y -> 0 <= x < modulus -> 0 <= y < modulus -> x = y. |
---|
678 | Proof (eqmod_small_eq modulus). |
---|
679 | Hint Resolve eqm_small_eq: ints. |
---|
680 | |
---|
681 | Lemma eqm_add: |
---|
682 | forall a b c d, eqm a b -> eqm c d -> eqm (a + c) (b + d). |
---|
683 | Proof (eqmod_add modulus). |
---|
684 | Hint Resolve eqm_add: ints. |
---|
685 | |
---|
686 | Lemma eqm_neg: |
---|
687 | forall x y, eqm x y -> eqm (-x) (-y). |
---|
688 | Proof (eqmod_neg modulus). |
---|
689 | Hint Resolve eqm_neg: ints. |
---|
690 | |
---|
691 | Lemma eqm_sub: |
---|
692 | forall a b c d, eqm a b -> eqm c d -> eqm (a - c) (b - d). |
---|
693 | Proof (eqmod_sub modulus). |
---|
694 | Hint Resolve eqm_sub: ints. |
---|
695 | |
---|
696 | Lemma eqm_mult: |
---|
697 | forall a b c d, eqm a c -> eqm b d -> eqm (a * b) (c * d). |
---|
698 | Proof (eqmod_mult modulus). |
---|
699 | Hint Resolve eqm_mult: ints. |
---|
700 | |
---|
701 | (** ** Properties of the coercions between [Z] and [int] *) |
---|
702 | |
---|
703 | Lemma eqm_unsigned_repr: |
---|
704 | forall z, eqm z (unsigned (repr z)). |
---|
705 | Proof. |
---|
706 | unfold eqm, repr, unsigned; intros; simpl. |
---|
707 | apply eqmod_mod. auto with ints. |
---|
708 | Qed. |
---|
709 | Hint Resolve eqm_unsigned_repr: ints. |
---|
710 | |
---|
711 | Lemma eqm_unsigned_repr_l: |
---|
712 | forall a b, eqm a b -> eqm (unsigned (repr a)) b. |
---|
713 | Proof. |
---|
714 | intros. apply eqm_trans with a. |
---|
715 | apply eqm_sym. apply eqm_unsigned_repr. auto. |
---|
716 | Qed. |
---|
717 | Hint Resolve eqm_unsigned_repr_l: ints. |
---|
718 | |
---|
719 | Lemma eqm_unsigned_repr_r: |
---|
720 | forall a b, eqm a b -> eqm a (unsigned (repr b)). |
---|
721 | Proof. |
---|
722 | intros. apply eqm_trans with b. auto. |
---|
723 | apply eqm_unsigned_repr. |
---|
724 | Qed. |
---|
725 | Hint Resolve eqm_unsigned_repr_r: ints. |
---|
726 | |
---|
727 | Lemma eqm_signed_unsigned: |
---|
728 | forall x, eqm (signed x) (unsigned x). |
---|
729 | Proof. |
---|
730 | intro; red; unfold signed. set (y := unsigned x). |
---|
731 | case (zlt y half_modulus); intro. |
---|
732 | apply eqmod_refl. red; exists (-1); ring. |
---|
733 | Qed. |
---|
734 | *) |
---|
735 | |
---|
736 | theorem unsigned_range: ∀i. 0 ≤ unsigned i ∧ unsigned i < modulus. |
---|
737 | #i cases i; #i' #H cases H; /2/; |
---|
738 | qed. |
---|
739 | |
---|
740 | theorem unsigned_range_2: |
---|
741 | ∀i. 0 ≤ unsigned i ∧ unsigned i ≤ max_unsigned. |
---|
742 | #i >(?:max_unsigned = modulus - 1) //; (* unfold *) |
---|
743 | lapply (unsigned_range i); *; #Hz #Hm % |
---|
744 | [ //; |
---|
745 | | <(Zpred_Zsucc (unsigned i)) |
---|
746 | <(Zpred_Zplus_neg_O modulus) |
---|
747 | @monotonic_Zle_Zpred |
---|
748 | /2/; |
---|
749 | ] qed. |
---|
750 | |
---|
751 | axiom signed_range: |
---|
752 | ∀i. min_signed ≤ signed i ∧ signed i ≤ max_signed. |
---|
753 | (* |
---|
754 | #i whd in ⊢ (?(??%)(?%?)); |
---|
755 | lapply (unsigned_range i); *; letin n ≝ (unsigned i); #H1 #H2 |
---|
756 | @(Zltb_elim_Type0) #H3 |
---|
757 | [ % [ @(transitive_Zle ? OZ) //; |
---|
758 | | <(Zpred_Zsucc n) |
---|
759 | <(Zpred_Zplus_neg_O half_modulus) |
---|
760 | @monotonic_Zle_Zpred /2/; |
---|
761 | ] |
---|
762 | | % [ >half_modulus_modulus |
---|
763 | |
---|
764 | Theorem signed_range: |
---|
765 | forall i, min_signed <= signed i <= max_signed. |
---|
766 | Proof. |
---|
767 | intros. unfold signed. |
---|
768 | generalize (unsigned_range i). set (n := unsigned i). intros. |
---|
769 | case (zlt n half_modulus); intro. |
---|
770 | unfold max_signed. generalize min_signed_neg. omega. |
---|
771 | unfold min_signed, max_signed. |
---|
772 | rewrite half_modulus_modulus in *. omega. |
---|
773 | Qed. |
---|
774 | |
---|
775 | Theorem repr_unsigned: |
---|
776 | forall i, repr (unsigned i) = i. |
---|
777 | Proof. |
---|
778 | destruct i; simpl. unfold repr. apply mkint_eq. |
---|
779 | apply Zmod_small. auto. |
---|
780 | Qed. |
---|
781 | Hint Resolve repr_unsigned: ints. |
---|
782 | |
---|
783 | Lemma repr_signed: |
---|
784 | forall i, repr (signed i) = i. |
---|
785 | Proof. |
---|
786 | intros. transitivity (repr (unsigned i)). |
---|
787 | apply eqm_samerepr. apply eqm_signed_unsigned. auto with ints. |
---|
788 | Qed. |
---|
789 | Hint Resolve repr_signed: ints. |
---|
790 | |
---|
791 | Theorem unsigned_repr: |
---|
792 | forall z, 0 <= z <= max_unsigned -> unsigned (repr z) = z. |
---|
793 | Proof. |
---|
794 | intros. unfold repr, unsigned; simpl. |
---|
795 | apply Zmod_small. unfold max_unsigned in H. omega. |
---|
796 | Qed. |
---|
797 | Hint Resolve unsigned_repr: ints. |
---|
798 | *) |
---|
799 | axiom signed_repr: |
---|
800 | ∀z. min_signed ≤ z ∧ z ≤ max_signed → signed (repr z) = z. |
---|
801 | (* |
---|
802 | Theorem signed_repr: |
---|
803 | forall z, min_signed <= z <= max_signed -> signed (repr z) = z. |
---|
804 | Proof. |
---|
805 | intros. unfold signed. case (zle 0 z); intro. |
---|
806 | replace (unsigned (repr z)) with z. |
---|
807 | rewrite zlt_true. auto. unfold max_signed in H. omega. |
---|
808 | symmetry. apply unsigned_repr. generalize max_signed_unsigned. omega. |
---|
809 | pose (z' := z + modulus). |
---|
810 | replace (repr z) with (repr z'). |
---|
811 | replace (unsigned (repr z')) with z'. |
---|
812 | rewrite zlt_false. unfold z'. omega. |
---|
813 | unfold z'. unfold min_signed in H. |
---|
814 | rewrite half_modulus_modulus. omega. |
---|
815 | symmetry. apply unsigned_repr. |
---|
816 | unfold z', max_unsigned. unfold min_signed, max_signed in H. |
---|
817 | rewrite half_modulus_modulus. omega. |
---|
818 | apply eqm_samerepr. unfold z'; red. exists 1. omega. |
---|
819 | Qed. |
---|
820 | |
---|
821 | Theorem signed_eq_unsigned: |
---|
822 | forall x, unsigned x <= max_signed -> signed x = unsigned x. |
---|
823 | Proof. |
---|
824 | intros. unfold signed. destruct (zlt (unsigned x) half_modulus). |
---|
825 | auto. unfold max_signed in H. omegaContradiction. |
---|
826 | Qed. |
---|
827 | |
---|
828 | (** ** Properties of addition *) |
---|
829 | |
---|
830 | *) |
---|
831 | axiom add_unsigned: ∀x,y. add x y = repr (unsigned x + unsigned y). |
---|
832 | axiom add_signed: ∀x,y. add x y = repr (signed x + signed y). |
---|
833 | axiom add_zero: ∀x. add x zero = x. |
---|
834 | |
---|
835 | (* |
---|
836 | Theorem add_unsigned: forall x y, add x y = repr (unsigned x + unsigned y). |
---|
837 | Proof. intros; reflexivity. |
---|
838 | Qed. |
---|
839 | |
---|
840 | Theorem add_signed: forall x y, add x y = repr (signed x + signed y). |
---|
841 | Proof. |
---|
842 | intros. rewrite add_unsigned. apply eqm_samerepr. |
---|
843 | apply eqm_add; apply eqm_sym; apply eqm_signed_unsigned. |
---|
844 | Qed. |
---|
845 | |
---|
846 | Theorem add_commut: forall x y, add x y = add y x. |
---|
847 | Proof. intros; unfold add. decEq. omega. Qed. |
---|
848 | |
---|
849 | Theorem add_zero: forall x, add x zero = x. |
---|
850 | Proof. |
---|
851 | intros; unfold add, zero. change (unsigned (repr 0)) with 0. |
---|
852 | rewrite Zplus_0_r. apply repr_unsigned. |
---|
853 | Qed. |
---|
854 | |
---|
855 | Theorem add_assoc: forall x y z, add (add x y) z = add x (add y z). |
---|
856 | Proof. |
---|
857 | intros; unfold add. |
---|
858 | set (x' := unsigned x). |
---|
859 | set (y' := unsigned y). |
---|
860 | set (z' := unsigned z). |
---|
861 | apply eqm_samerepr. |
---|
862 | apply eqm_trans with ((x' + y') + z'). |
---|
863 | auto with ints. |
---|
864 | rewrite <- Zplus_assoc. auto with ints. |
---|
865 | Qed. |
---|
866 | |
---|
867 | Theorem add_permut: forall x y z, add x (add y z) = add y (add x z). |
---|
868 | Proof. |
---|
869 | intros. rewrite (add_commut y z). rewrite <- add_assoc. apply add_commut. |
---|
870 | Qed. |
---|
871 | |
---|
872 | Theorem add_neg_zero: forall x, add x (neg x) = zero. |
---|
873 | Proof. |
---|
874 | intros; unfold add, neg, zero. apply eqm_samerepr. |
---|
875 | replace 0 with (unsigned x + (- (unsigned x))). |
---|
876 | auto with ints. omega. |
---|
877 | Qed. |
---|
878 | |
---|
879 | (** ** Properties of negation *) |
---|
880 | |
---|
881 | Theorem neg_repr: forall z, neg (repr z) = repr (-z). |
---|
882 | Proof. |
---|
883 | intros; unfold neg. apply eqm_samerepr. auto with ints. |
---|
884 | Qed. |
---|
885 | |
---|
886 | Theorem neg_zero: neg zero = zero. |
---|
887 | Proof. |
---|
888 | unfold neg, zero. compute. apply mkint_eq. auto. |
---|
889 | Qed. |
---|
890 | |
---|
891 | Theorem neg_involutive: forall x, neg (neg x) = x. |
---|
892 | Proof. |
---|
893 | intros; unfold neg. transitivity (repr (unsigned x)). |
---|
894 | apply eqm_samerepr. apply eqm_trans with (- (- (unsigned x))). |
---|
895 | apply eqm_neg. apply eqm_unsigned_repr_l. apply eqm_refl. |
---|
896 | apply eqm_refl2. omega. apply repr_unsigned. |
---|
897 | Qed. |
---|
898 | |
---|
899 | Theorem neg_add_distr: forall x y, neg(add x y) = add (neg x) (neg y). |
---|
900 | Proof. |
---|
901 | intros; unfold neg, add. apply eqm_samerepr. |
---|
902 | apply eqm_trans with (- (unsigned x + unsigned y)). |
---|
903 | auto with ints. |
---|
904 | replace (- (unsigned x + unsigned y)) |
---|
905 | with ((- unsigned x) + (- unsigned y)). |
---|
906 | auto with ints. omega. |
---|
907 | Qed. |
---|
908 | |
---|
909 | (** ** Properties of subtraction *) |
---|
910 | |
---|
911 | Theorem sub_zero_l: forall x, sub x zero = x. |
---|
912 | Proof. |
---|
913 | intros; unfold sub. change (unsigned zero) with 0. |
---|
914 | replace (unsigned x - 0) with (unsigned x). apply repr_unsigned. |
---|
915 | omega. |
---|
916 | Qed. |
---|
917 | |
---|
918 | Theorem sub_zero_r: forall x, sub zero x = neg x. |
---|
919 | Proof. |
---|
920 | intros; unfold sub, neg. change (unsigned zero) with 0. |
---|
921 | replace (0 - unsigned x) with (- unsigned x). auto. |
---|
922 | omega. |
---|
923 | Qed. |
---|
924 | |
---|
925 | Theorem sub_add_opp: forall x y, sub x y = add x (neg y). |
---|
926 | Proof. |
---|
927 | intros; unfold sub, add, neg. |
---|
928 | replace (unsigned x - unsigned y) |
---|
929 | with (unsigned x + (- unsigned y)). |
---|
930 | apply eqm_samerepr. auto with ints. omega. |
---|
931 | Qed. |
---|
932 | |
---|
933 | Theorem sub_idem: forall x, sub x x = zero. |
---|
934 | Proof. |
---|
935 | intros; unfold sub. replace (unsigned x - unsigned x) with 0. |
---|
936 | reflexivity. omega. |
---|
937 | Qed. |
---|
938 | |
---|
939 | Theorem sub_add_l: forall x y z, sub (add x y) z = add (sub x z) y. |
---|
940 | Proof. |
---|
941 | intros. repeat rewrite sub_add_opp. |
---|
942 | repeat rewrite add_assoc. decEq. apply add_commut. |
---|
943 | Qed. |
---|
944 | |
---|
945 | Theorem sub_add_r: forall x y z, sub x (add y z) = add (sub x z) (neg y). |
---|
946 | Proof. |
---|
947 | intros. repeat rewrite sub_add_opp. |
---|
948 | rewrite neg_add_distr. rewrite add_permut. apply add_commut. |
---|
949 | Qed. |
---|
950 | |
---|
951 | Theorem sub_shifted: |
---|
952 | forall x y z, |
---|
953 | sub (add x z) (add y z) = sub x y. |
---|
954 | Proof. |
---|
955 | intros. rewrite sub_add_opp. rewrite neg_add_distr. |
---|
956 | rewrite add_assoc. |
---|
957 | rewrite (add_commut (neg y) (neg z)). |
---|
958 | rewrite <- (add_assoc z). rewrite add_neg_zero. |
---|
959 | rewrite (add_commut zero). rewrite add_zero. |
---|
960 | symmetry. apply sub_add_opp. |
---|
961 | Qed. |
---|
962 | |
---|
963 | Theorem sub_signed: |
---|
964 | forall x y, sub x y = repr (signed x - signed y). |
---|
965 | Proof. |
---|
966 | intros. unfold sub. apply eqm_samerepr. |
---|
967 | apply eqm_sub; apply eqm_sym; apply eqm_signed_unsigned. |
---|
968 | Qed. |
---|
969 | |
---|
970 | (** ** Properties of multiplication *) |
---|
971 | |
---|
972 | Theorem mul_commut: forall x y, mul x y = mul y x. |
---|
973 | Proof. |
---|
974 | intros; unfold mul. decEq. ring. |
---|
975 | Qed. |
---|
976 | |
---|
977 | Theorem mul_zero: forall x, mul x zero = zero. |
---|
978 | Proof. |
---|
979 | intros; unfold mul. change (unsigned zero) with 0. |
---|
980 | unfold zero. decEq. ring. |
---|
981 | Qed. |
---|
982 | |
---|
983 | Theorem mul_one: forall x, mul x one = x. |
---|
984 | Proof. |
---|
985 | intros; unfold mul. rewrite unsigned_one. |
---|
986 | transitivity (repr (unsigned x)). decEq. ring. |
---|
987 | apply repr_unsigned. |
---|
988 | Qed. |
---|
989 | |
---|
990 | Theorem mul_assoc: forall x y z, mul (mul x y) z = mul x (mul y z). |
---|
991 | Proof. |
---|
992 | intros; unfold mul. |
---|
993 | set (x' := unsigned x). |
---|
994 | set (y' := unsigned y). |
---|
995 | set (z' := unsigned z). |
---|
996 | apply eqm_samerepr. apply eqm_trans with ((x' * y') * z'). |
---|
997 | auto with ints. |
---|
998 | rewrite <- Zmult_assoc. auto with ints. |
---|
999 | Qed. |
---|
1000 | |
---|
1001 | Theorem mul_add_distr_l: |
---|
1002 | forall x y z, mul (add x y) z = add (mul x z) (mul y z). |
---|
1003 | Proof. |
---|
1004 | intros; unfold mul, add. |
---|
1005 | apply eqm_samerepr. |
---|
1006 | set (x' := unsigned x). |
---|
1007 | set (y' := unsigned y). |
---|
1008 | set (z' := unsigned z). |
---|
1009 | apply eqm_trans with ((x' + y') * z'). |
---|
1010 | auto with ints. |
---|
1011 | replace ((x' + y') * z') with (x' * z' + y' * z'). |
---|
1012 | auto with ints. |
---|
1013 | ring. |
---|
1014 | Qed. |
---|
1015 | |
---|
1016 | Theorem mul_add_distr_r: |
---|
1017 | forall x y z, mul x (add y z) = add (mul x y) (mul x z). |
---|
1018 | Proof. |
---|
1019 | intros. rewrite mul_commut. rewrite mul_add_distr_l. |
---|
1020 | decEq; apply mul_commut. |
---|
1021 | Qed. |
---|
1022 | |
---|
1023 | Theorem neg_mul_distr_l: |
---|
1024 | forall x y, neg(mul x y) = mul (neg x) y. |
---|
1025 | Proof. |
---|
1026 | intros. unfold mul, neg. |
---|
1027 | set (x' := unsigned x). set (y' := unsigned y). |
---|
1028 | apply eqm_samerepr. apply eqm_trans with (- (x' * y')). |
---|
1029 | auto with ints. |
---|
1030 | replace (- (x' * y')) with ((-x') * y') by ring. |
---|
1031 | auto with ints. |
---|
1032 | Qed. |
---|
1033 | |
---|
1034 | Theorem neg_mul_distr_r: |
---|
1035 | forall x y, neg(mul x y) = mul x (neg y). |
---|
1036 | Proof. |
---|
1037 | intros. rewrite (mul_commut x y). rewrite (mul_commut x (neg y)). |
---|
1038 | apply neg_mul_distr_l. |
---|
1039 | Qed. |
---|
1040 | |
---|
1041 | Theorem mul_signed: |
---|
1042 | forall x y, mul x y = repr (signed x * signed y). |
---|
1043 | Proof. |
---|
1044 | intros; unfold mul. apply eqm_samerepr. |
---|
1045 | apply eqm_mult; apply eqm_sym; apply eqm_signed_unsigned. |
---|
1046 | Qed. |
---|
1047 | |
---|
1048 | (** ** Properties of binary decompositions *) |
---|
1049 | |
---|
1050 | Lemma Z_shift_add_bin_decomp: |
---|
1051 | forall x, |
---|
1052 | Z_shift_add (fst (Z_bin_decomp x)) (snd (Z_bin_decomp x)) = x. |
---|
1053 | Proof. |
---|
1054 | destruct x; simpl. |
---|
1055 | auto. |
---|
1056 | destruct p; reflexivity. |
---|
1057 | destruct p; try reflexivity. simpl. |
---|
1058 | assert (forall z, 2 * (z + 1) - 1 = 2 * z + 1). intro; omega. |
---|
1059 | generalize (H (Zpos p)); simpl. congruence. |
---|
1060 | Qed. |
---|
1061 | |
---|
1062 | Lemma Z_shift_add_inj: |
---|
1063 | forall b1 x1 b2 x2, |
---|
1064 | Z_shift_add b1 x1 = Z_shift_add b2 x2 -> b1 = b2 /\ x1 = x2. |
---|
1065 | Proof. |
---|
1066 | intros until x2. |
---|
1067 | unfold Z_shift_add. |
---|
1068 | destruct b1; destruct b2; intros; |
---|
1069 | ((split; [reflexivity|omega]) || omegaContradiction). |
---|
1070 | Qed. |
---|
1071 | |
---|
1072 | Lemma Z_of_bits_exten: |
---|
1073 | forall n f1 f2, |
---|
1074 | (forall z, 0 <= z < Z_of_nat n -> f1 z = f2 z) -> |
---|
1075 | Z_of_bits n f1 = Z_of_bits n f2. |
---|
1076 | Proof. |
---|
1077 | induction n; intros. |
---|
1078 | reflexivity. |
---|
1079 | simpl. rewrite inj_S in H. decEq. apply H. omega. |
---|
1080 | apply IHn. intros; apply H. omega. |
---|
1081 | Qed. |
---|
1082 | |
---|
1083 | Opaque Zmult. |
---|
1084 | |
---|
1085 | Lemma Z_of_bits_of_Z: |
---|
1086 | forall x, eqm (Z_of_bits wordsize (bits_of_Z wordsize x)) x. |
---|
1087 | Proof. |
---|
1088 | assert (forall n x, exists k, |
---|
1089 | Z_of_bits n (bits_of_Z n x) = k * two_power_nat n + x). |
---|
1090 | induction n; intros. |
---|
1091 | rewrite two_power_nat_O. simpl. exists (-x). omega. |
---|
1092 | rewrite two_power_nat_S. simpl. |
---|
1093 | caseEq (Z_bin_decomp x). intros b y ZBD. simpl. |
---|
1094 | replace (Z_of_bits n (fun i => if zeq (i + 1) 0 then b else bits_of_Z n y (i + 1 - 1))) |
---|
1095 | with (Z_of_bits n (bits_of_Z n y)). |
---|
1096 | elim (IHn y). intros k1 EQ1. rewrite EQ1. |
---|
1097 | rewrite <- (Z_shift_add_bin_decomp x). |
---|
1098 | rewrite ZBD. simpl. |
---|
1099 | exists k1. |
---|
1100 | case b; unfold Z_shift_add; ring. |
---|
1101 | apply Z_of_bits_exten. intros. |
---|
1102 | rewrite zeq_false. decEq. omega. omega. |
---|
1103 | intro. exact (H wordsize x). |
---|
1104 | Qed. |
---|
1105 | |
---|
1106 | Lemma bits_of_Z_zero: |
---|
1107 | forall n x, bits_of_Z n 0 x = false. |
---|
1108 | Proof. |
---|
1109 | induction n; simpl; intros. |
---|
1110 | auto. |
---|
1111 | case (zeq x 0); intro. auto. auto. |
---|
1112 | Qed. |
---|
1113 | |
---|
1114 | Remark Z_bin_decomp_2xm1: |
---|
1115 | forall x, Z_bin_decomp (2 * x - 1) = (true, x - 1). |
---|
1116 | Proof. |
---|
1117 | intros. caseEq (Z_bin_decomp (2 * x - 1)). intros b y EQ. |
---|
1118 | generalize (Z_shift_add_bin_decomp (2 * x - 1)). |
---|
1119 | rewrite EQ; simpl. |
---|
1120 | replace (2 * x - 1) with (Z_shift_add true (x - 1)). |
---|
1121 | intro. elim (Z_shift_add_inj _ _ _ _ H); intros. |
---|
1122 | congruence. unfold Z_shift_add. omega. |
---|
1123 | Qed. |
---|
1124 | |
---|
1125 | Lemma bits_of_Z_mone: |
---|
1126 | forall n x, |
---|
1127 | 0 <= x < Z_of_nat n -> |
---|
1128 | bits_of_Z n (two_power_nat n - 1) x = true. |
---|
1129 | Proof. |
---|
1130 | induction n; intros. |
---|
1131 | simpl in H. omegaContradiction. |
---|
1132 | unfold bits_of_Z; fold bits_of_Z. |
---|
1133 | rewrite two_power_nat_S. rewrite Z_bin_decomp_2xm1. |
---|
1134 | rewrite inj_S in H. case (zeq x 0); intro. auto. |
---|
1135 | apply IHn. omega. |
---|
1136 | Qed. |
---|
1137 | |
---|
1138 | Lemma Z_bin_decomp_shift_add: |
---|
1139 | forall b x, Z_bin_decomp (Z_shift_add b x) = (b, x). |
---|
1140 | Proof. |
---|
1141 | intros. caseEq (Z_bin_decomp (Z_shift_add b x)); intros b' x' EQ. |
---|
1142 | generalize (Z_shift_add_bin_decomp (Z_shift_add b x)). |
---|
1143 | rewrite EQ; simpl fst; simpl snd. intro. |
---|
1144 | elim (Z_shift_add_inj _ _ _ _ H); intros. |
---|
1145 | congruence. |
---|
1146 | Qed. |
---|
1147 | |
---|
1148 | Lemma bits_of_Z_of_bits: |
---|
1149 | forall n f i, |
---|
1150 | 0 <= i < Z_of_nat n -> |
---|
1151 | bits_of_Z n (Z_of_bits n f) i = f i. |
---|
1152 | Proof. |
---|
1153 | induction n; intros; simpl. |
---|
1154 | simpl in H. omegaContradiction. |
---|
1155 | rewrite Z_bin_decomp_shift_add. |
---|
1156 | case (zeq i 0); intro. |
---|
1157 | congruence. |
---|
1158 | rewrite IHn. decEq. omega. rewrite inj_S in H. omega. |
---|
1159 | Qed. |
---|
1160 | |
---|
1161 | Lemma Z_of_bits_range: |
---|
1162 | forall f, 0 <= Z_of_bits wordsize f < modulus. |
---|
1163 | Proof. |
---|
1164 | unfold max_unsigned, modulus. |
---|
1165 | generalize wordsize. induction n; simpl; intros. |
---|
1166 | rewrite two_power_nat_O. omega. |
---|
1167 | rewrite two_power_nat_S. generalize (IHn (fun i => f (i + 1))). |
---|
1168 | set (x := Z_of_bits n (fun i => f (i + 1))). |
---|
1169 | intro. destruct (f 0); unfold Z_shift_add; omega. |
---|
1170 | Qed. |
---|
1171 | Hint Resolve Z_of_bits_range: ints. |
---|
1172 | |
---|
1173 | Lemma Z_of_bits_range_2: |
---|
1174 | forall f, 0 <= Z_of_bits wordsize f <= max_unsigned. |
---|
1175 | Proof. |
---|
1176 | intros. unfold max_unsigned. |
---|
1177 | generalize (Z_of_bits_range f). omega. |
---|
1178 | Qed. |
---|
1179 | Hint Resolve Z_of_bits_range_2: ints. |
---|
1180 | |
---|
1181 | Lemma bits_of_Z_below: |
---|
1182 | forall n x i, i < 0 -> bits_of_Z n x i = false. |
---|
1183 | Proof. |
---|
1184 | induction n; simpl; intros. |
---|
1185 | reflexivity. |
---|
1186 | destruct (Z_bin_decomp x). rewrite zeq_false. apply IHn. |
---|
1187 | omega. omega. |
---|
1188 | Qed. |
---|
1189 | |
---|
1190 | Lemma bits_of_Z_above: |
---|
1191 | forall n x i, i >= Z_of_nat n -> bits_of_Z n x i = false. |
---|
1192 | Proof. |
---|
1193 | induction n; intros; simpl. |
---|
1194 | reflexivity. |
---|
1195 | destruct (Z_bin_decomp x). rewrite zeq_false. apply IHn. |
---|
1196 | rewrite inj_S in H. omega. rewrite inj_S in H. omega. |
---|
1197 | Qed. |
---|
1198 | |
---|
1199 | Lemma bits_of_Z_of_bits': |
---|
1200 | forall n f i, |
---|
1201 | bits_of_Z n (Z_of_bits n f) i = |
---|
1202 | if zlt i 0 then false |
---|
1203 | else if zle (Z_of_nat n) i then false |
---|
1204 | else f i. |
---|
1205 | Proof. |
---|
1206 | intros. |
---|
1207 | destruct (zlt i 0). apply bits_of_Z_below; auto. |
---|
1208 | destruct (zle (Z_of_nat n) i). apply bits_of_Z_above. omega. |
---|
1209 | apply bits_of_Z_of_bits. omega. |
---|
1210 | Qed. |
---|
1211 | |
---|
1212 | Opaque Zmult. |
---|
1213 | |
---|
1214 | Lemma Z_of_bits_excl: |
---|
1215 | forall n f g h, |
---|
1216 | (forall i, 0 <= i < Z_of_nat n -> f i && g i = false) -> |
---|
1217 | (forall i, 0 <= i < Z_of_nat n -> f i || g i = h i) -> |
---|
1218 | Z_of_bits n f + Z_of_bits n g = Z_of_bits n h. |
---|
1219 | Proof. |
---|
1220 | induction n. |
---|
1221 | intros; reflexivity. |
---|
1222 | intros. simpl. rewrite inj_S in H. rewrite inj_S in H0. |
---|
1223 | rewrite <- (IHn (fun i => f(i+1)) (fun i => g(i+1)) (fun i => h(i+1))). |
---|
1224 | assert (0 <= 0 < Zsucc(Z_of_nat n)). omega. |
---|
1225 | unfold Z_shift_add. |
---|
1226 | rewrite <- H0; auto. |
---|
1227 | set (F := Z_of_bits n (fun i => f(i + 1))). |
---|
1228 | set (G := Z_of_bits n (fun i => g(i + 1))). |
---|
1229 | caseEq (f 0); intros; caseEq (g 0); intros; simpl. |
---|
1230 | generalize (H 0 H1). rewrite H2; rewrite H3. simpl. intros; discriminate. |
---|
1231 | omega. omega. omega. |
---|
1232 | intros; apply H. omega. |
---|
1233 | intros; apply H0. omega. |
---|
1234 | Qed. |
---|
1235 | |
---|
1236 | (** ** Properties of bitwise and, or, xor *) |
---|
1237 | |
---|
1238 | Lemma bitwise_binop_commut: |
---|
1239 | forall f, |
---|
1240 | (forall a b, f a b = f b a) -> |
---|
1241 | forall x y, |
---|
1242 | bitwise_binop f x y = bitwise_binop f y x. |
---|
1243 | Proof. |
---|
1244 | unfold bitwise_binop; intros. |
---|
1245 | decEq. apply Z_of_bits_exten; intros. auto. |
---|
1246 | Qed. |
---|
1247 | |
---|
1248 | Lemma bitwise_binop_assoc: |
---|
1249 | forall f, |
---|
1250 | (forall a b c, f a (f b c) = f (f a b) c) -> |
---|
1251 | forall x y z, |
---|
1252 | bitwise_binop f (bitwise_binop f x y) z = |
---|
1253 | bitwise_binop f x (bitwise_binop f y z). |
---|
1254 | Proof. |
---|
1255 | unfold bitwise_binop; intros. |
---|
1256 | repeat rewrite unsigned_repr; auto with ints. |
---|
1257 | decEq. apply Z_of_bits_exten; intros. |
---|
1258 | repeat (rewrite bits_of_Z_of_bits; auto). |
---|
1259 | Qed. |
---|
1260 | |
---|
1261 | Lemma bitwise_binop_idem: |
---|
1262 | forall f, |
---|
1263 | (forall a, f a a = a) -> |
---|
1264 | forall x, |
---|
1265 | bitwise_binop f x x = x. |
---|
1266 | Proof. |
---|
1267 | unfold bitwise_binop; intros. |
---|
1268 | transitivity (repr (Z_of_bits wordsize (bits_of_Z wordsize (unsigned x)))). |
---|
1269 | decEq. apply Z_of_bits_exten; intros. auto. |
---|
1270 | transitivity (repr (unsigned x)). |
---|
1271 | apply eqm_samerepr. apply Z_of_bits_of_Z. apply repr_unsigned. |
---|
1272 | Qed. |
---|
1273 | |
---|
1274 | Theorem and_commut: forall x y, and x y = and y x. |
---|
1275 | Proof (bitwise_binop_commut andb andb_comm). |
---|
1276 | |
---|
1277 | Theorem and_assoc: forall x y z, and (and x y) z = and x (and y z). |
---|
1278 | Proof (bitwise_binop_assoc andb andb_assoc). |
---|
1279 | |
---|
1280 | Theorem and_zero: forall x, and x zero = zero. |
---|
1281 | Proof. |
---|
1282 | intros. unfold and, bitwise_binop. |
---|
1283 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1284 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1285 | rewrite unsigned_zero. rewrite bits_of_Z_zero. apply andb_b_false. |
---|
1286 | Qed. |
---|
1287 | |
---|
1288 | Theorem and_mone: forall x, and x mone = x. |
---|
1289 | Proof. |
---|
1290 | intros. unfold and, bitwise_binop. |
---|
1291 | transitivity (repr(unsigned x)). |
---|
1292 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1293 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1294 | rewrite unsigned_mone. rewrite bits_of_Z_mone. apply andb_b_true. auto. |
---|
1295 | apply repr_unsigned. |
---|
1296 | Qed. |
---|
1297 | |
---|
1298 | Theorem and_idem: forall x, and x x = x. |
---|
1299 | Proof. |
---|
1300 | assert (forall b, b && b = b). |
---|
1301 | destruct b; reflexivity. |
---|
1302 | exact (bitwise_binop_idem andb H). |
---|
1303 | Qed. |
---|
1304 | |
---|
1305 | Theorem or_commut: forall x y, or x y = or y x. |
---|
1306 | Proof (bitwise_binop_commut orb orb_comm). |
---|
1307 | |
---|
1308 | Theorem or_assoc: forall x y z, or (or x y) z = or x (or y z). |
---|
1309 | Proof (bitwise_binop_assoc orb orb_assoc). |
---|
1310 | |
---|
1311 | Theorem or_zero: forall x, or x zero = x. |
---|
1312 | Proof. |
---|
1313 | intros. unfold or, bitwise_binop. |
---|
1314 | transitivity (repr(unsigned x)). |
---|
1315 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1316 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1317 | rewrite unsigned_zero. rewrite bits_of_Z_zero. apply orb_b_false. |
---|
1318 | apply repr_unsigned. |
---|
1319 | Qed. |
---|
1320 | |
---|
1321 | Theorem or_mone: forall x, or x mone = mone. |
---|
1322 | Proof. |
---|
1323 | intros. unfold or, bitwise_binop. |
---|
1324 | transitivity (repr(unsigned mone)). |
---|
1325 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1326 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1327 | rewrite unsigned_mone. rewrite bits_of_Z_mone. apply orb_b_true. auto. |
---|
1328 | apply repr_unsigned. |
---|
1329 | Qed. |
---|
1330 | |
---|
1331 | Theorem or_idem: forall x, or x x = x. |
---|
1332 | Proof. |
---|
1333 | assert (forall b, b || b = b). |
---|
1334 | destruct b; reflexivity. |
---|
1335 | exact (bitwise_binop_idem orb H). |
---|
1336 | Qed. |
---|
1337 | |
---|
1338 | Theorem and_or_distrib: |
---|
1339 | forall x y z, |
---|
1340 | and x (or y z) = or (and x y) (and x z). |
---|
1341 | Proof. |
---|
1342 | intros; unfold and, or, bitwise_binop. |
---|
1343 | decEq. repeat rewrite unsigned_repr; auto with ints. |
---|
1344 | apply Z_of_bits_exten; intros. |
---|
1345 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1346 | apply demorgan1. |
---|
1347 | Qed. |
---|
1348 | |
---|
1349 | Theorem xor_commut: forall x y, xor x y = xor y x. |
---|
1350 | Proof (bitwise_binop_commut xorb xorb_comm). |
---|
1351 | |
---|
1352 | Theorem xor_assoc: forall x y z, xor (xor x y) z = xor x (xor y z). |
---|
1353 | Proof. |
---|
1354 | assert (forall a b c, xorb a (xorb b c) = xorb (xorb a b) c). |
---|
1355 | symmetry. apply xorb_assoc. |
---|
1356 | exact (bitwise_binop_assoc xorb H). |
---|
1357 | Qed. |
---|
1358 | |
---|
1359 | Theorem xor_zero: forall x, xor x zero = x. |
---|
1360 | Proof. |
---|
1361 | intros. unfold xor, bitwise_binop. |
---|
1362 | transitivity (repr(unsigned x)). |
---|
1363 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1364 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1365 | rewrite unsigned_zero. rewrite bits_of_Z_zero. apply xorb_false. |
---|
1366 | apply repr_unsigned. |
---|
1367 | Qed. |
---|
1368 | |
---|
1369 | Theorem xor_idem: forall x, xor x x = zero. |
---|
1370 | Proof. |
---|
1371 | intros. unfold xor, bitwise_binop. |
---|
1372 | transitivity (repr(unsigned zero)). |
---|
1373 | apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1374 | apply eqm_refl2. apply Z_of_bits_exten. intros. |
---|
1375 | rewrite unsigned_zero. rewrite bits_of_Z_zero. apply xorb_nilpotent. |
---|
1376 | apply repr_unsigned. |
---|
1377 | Qed. |
---|
1378 | |
---|
1379 | Theorem xor_zero_one: xor zero one = one. |
---|
1380 | Proof. rewrite xor_commut. apply xor_zero. Qed. |
---|
1381 | |
---|
1382 | Theorem xor_one_one: xor one one = zero. |
---|
1383 | Proof. apply xor_idem. Qed. |
---|
1384 | |
---|
1385 | Theorem and_xor_distrib: |
---|
1386 | forall x y z, |
---|
1387 | and x (xor y z) = xor (and x y) (and x z). |
---|
1388 | Proof. |
---|
1389 | intros; unfold and, xor, bitwise_binop. |
---|
1390 | decEq. repeat rewrite unsigned_repr; auto with ints. |
---|
1391 | apply Z_of_bits_exten; intros. |
---|
1392 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1393 | assert (forall a b c, a && (xorb b c) = xorb (a && b) (a && c)). |
---|
1394 | destruct a; destruct b; destruct c; reflexivity. |
---|
1395 | auto. |
---|
1396 | Qed. |
---|
1397 | |
---|
1398 | Theorem not_involutive: |
---|
1399 | forall (x: int), not (not x) = x. |
---|
1400 | Proof. |
---|
1401 | intros. unfold not. rewrite xor_assoc. rewrite xor_idem. apply xor_zero. |
---|
1402 | Qed. |
---|
1403 | |
---|
1404 | (** ** Properties of shifts and rotates *) |
---|
1405 | |
---|
1406 | Lemma Z_of_bits_shift: |
---|
1407 | forall n f, |
---|
1408 | exists k, |
---|
1409 | Z_of_bits n (fun i => f (i - 1)) = |
---|
1410 | k * two_power_nat n + Z_shift_add (f (-1)) (Z_of_bits n f). |
---|
1411 | Proof. |
---|
1412 | induction n; intros. |
---|
1413 | simpl. rewrite two_power_nat_O. unfold Z_shift_add. |
---|
1414 | exists (if f (-1) then (-1) else 0). |
---|
1415 | destruct (f (-1)); omega. |
---|
1416 | rewrite two_power_nat_S. simpl. |
---|
1417 | elim (IHn (fun i => f (i + 1))). intros k' EQ. |
---|
1418 | replace (Z_of_bits n (fun i => f (i - 1 + 1))) |
---|
1419 | with (Z_of_bits n (fun i => f (i + 1 - 1))) in EQ. |
---|
1420 | rewrite EQ. |
---|
1421 | change (-1 + 1) with 0. |
---|
1422 | exists k'. |
---|
1423 | unfold Z_shift_add; destruct (f (-1)); destruct (f 0); ring. |
---|
1424 | apply Z_of_bits_exten; intros. |
---|
1425 | decEq. omega. |
---|
1426 | Qed. |
---|
1427 | |
---|
1428 | Lemma Z_of_bits_shifts: |
---|
1429 | forall m f, |
---|
1430 | 0 <= m -> |
---|
1431 | (forall i, i < 0 -> f i = false) -> |
---|
1432 | eqm (Z_of_bits wordsize (fun i => f (i - m))) |
---|
1433 | (two_p m * Z_of_bits wordsize f). |
---|
1434 | Proof. |
---|
1435 | intros. pattern m. apply natlike_ind. |
---|
1436 | apply eqm_refl2. transitivity (Z_of_bits wordsize f). |
---|
1437 | apply Z_of_bits_exten; intros. decEq. omega. |
---|
1438 | simpl two_p. omega. |
---|
1439 | intros. rewrite two_p_S; auto. |
---|
1440 | set (f' := fun i => f (i - x)). |
---|
1441 | apply eqm_trans with (Z_of_bits wordsize (fun i => f' (i - 1))). |
---|
1442 | apply eqm_refl2. apply Z_of_bits_exten; intros. |
---|
1443 | unfold f'. decEq. omega. |
---|
1444 | apply eqm_trans with (Z_shift_add (f' (-1)) (Z_of_bits wordsize f')). |
---|
1445 | exact (Z_of_bits_shift wordsize f'). |
---|
1446 | unfold f'. unfold Z_shift_add. rewrite H0. |
---|
1447 | rewrite <- Zmult_assoc. apply eqm_mult. apply eqm_refl. |
---|
1448 | apply H2. omega. assumption. |
---|
1449 | Qed. |
---|
1450 | |
---|
1451 | Lemma shl_mul_two_p: |
---|
1452 | forall x y, |
---|
1453 | shl x y = mul x (repr (two_p (unsigned y))). |
---|
1454 | Proof. |
---|
1455 | intros. unfold shl, mul. |
---|
1456 | apply eqm_samerepr. |
---|
1457 | eapply eqm_trans. |
---|
1458 | apply Z_of_bits_shifts. |
---|
1459 | generalize (unsigned_range y). omega. |
---|
1460 | intros; apply bits_of_Z_below; auto. |
---|
1461 | rewrite Zmult_comm. apply eqm_mult. |
---|
1462 | apply Z_of_bits_of_Z. apply eqm_unsigned_repr. |
---|
1463 | Qed. |
---|
1464 | |
---|
1465 | Theorem shl_zero: forall x, shl x zero = x. |
---|
1466 | Proof. |
---|
1467 | intros. rewrite shl_mul_two_p. |
---|
1468 | change (repr (two_p (unsigned zero))) with one. |
---|
1469 | apply mul_one. |
---|
1470 | Qed. |
---|
1471 | |
---|
1472 | Theorem shl_mul: |
---|
1473 | forall x y, |
---|
1474 | shl x y = mul x (shl one y). |
---|
1475 | Proof. |
---|
1476 | intros. |
---|
1477 | assert (shl one y = repr (two_p (unsigned y))). |
---|
1478 | rewrite shl_mul_two_p. rewrite mul_commut. rewrite mul_one. auto. |
---|
1479 | rewrite H. apply shl_mul_two_p. |
---|
1480 | Qed. |
---|
1481 | |
---|
1482 | Lemma ltu_inv: |
---|
1483 | forall x y, ltu x y = true -> 0 <= unsigned x < unsigned y. |
---|
1484 | Proof. |
---|
1485 | unfold ltu; intros. destruct (zlt (unsigned x) (unsigned y)). |
---|
1486 | split; auto. generalize (unsigned_range x); omega. |
---|
1487 | discriminate. |
---|
1488 | Qed. |
---|
1489 | |
---|
1490 | Theorem shl_rolm: |
---|
1491 | forall x n, |
---|
1492 | ltu n iwordsize = true -> |
---|
1493 | shl x n = rolm x n (shl mone n). |
---|
1494 | Proof. |
---|
1495 | intros. exploit ltu_inv; eauto. rewrite unsigned_repr_wordsize; intros. |
---|
1496 | unfold shl, rolm, rol, and, bitwise_binop. |
---|
1497 | decEq. apply Z_of_bits_exten; intros. |
---|
1498 | repeat rewrite unsigned_repr; auto with ints. |
---|
1499 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1500 | case (zlt z (unsigned n)); intro LT2. |
---|
1501 | assert (z - unsigned n < 0). omega. |
---|
1502 | rewrite (bits_of_Z_below wordsize (unsigned x) _ H2). |
---|
1503 | rewrite (bits_of_Z_below wordsize (unsigned mone) _ H2). |
---|
1504 | symmetry. apply andb_b_false. |
---|
1505 | assert (z - unsigned n < Z_of_nat wordsize). |
---|
1506 | generalize (unsigned_range n). omega. |
---|
1507 | rewrite unsigned_mone. |
---|
1508 | rewrite bits_of_Z_mone. rewrite andb_b_true. decEq. |
---|
1509 | rewrite Zmod_small. auto. omega. omega. |
---|
1510 | Qed. |
---|
1511 | |
---|
1512 | Lemma bitwise_binop_shl: |
---|
1513 | forall f x y n, |
---|
1514 | f false false = false -> |
---|
1515 | bitwise_binop f (shl x n) (shl y n) = shl (bitwise_binop f x y) n. |
---|
1516 | Proof. |
---|
1517 | intros. unfold bitwise_binop, shl. |
---|
1518 | decEq. repeat rewrite unsigned_repr; auto with ints. |
---|
1519 | apply Z_of_bits_exten; intros. |
---|
1520 | case (zlt (z - unsigned n) 0); intro. |
---|
1521 | transitivity false. repeat rewrite bits_of_Z_of_bits; auto. |
---|
1522 | repeat rewrite bits_of_Z_below; auto. |
---|
1523 | rewrite bits_of_Z_below; auto. |
---|
1524 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1525 | generalize (unsigned_range n). omega. |
---|
1526 | Qed. |
---|
1527 | |
---|
1528 | Theorem and_shl: |
---|
1529 | forall x y n, |
---|
1530 | and (shl x n) (shl y n) = shl (and x y) n. |
---|
1531 | Proof. |
---|
1532 | unfold and; intros. apply bitwise_binop_shl. reflexivity. |
---|
1533 | Qed. |
---|
1534 | |
---|
1535 | |
---|
1536 | Theorem shl_shl: |
---|
1537 | forall x y z, |
---|
1538 | ltu y iwordsize = true -> |
---|
1539 | ltu z iwordsize = true -> |
---|
1540 | ltu (add y z) iwordsize = true -> |
---|
1541 | shl (shl x y) z = shl x (add y z). |
---|
1542 | Proof. |
---|
1543 | intros. unfold shl, add. |
---|
1544 | generalize (ltu_inv _ _ H). |
---|
1545 | generalize (ltu_inv _ _ H0). |
---|
1546 | rewrite unsigned_repr_wordsize. |
---|
1547 | set (x' := unsigned x). |
---|
1548 | set (y' := unsigned y). |
---|
1549 | set (z' := unsigned z). |
---|
1550 | intros. |
---|
1551 | repeat rewrite unsigned_repr. |
---|
1552 | decEq. apply Z_of_bits_exten. intros n R. |
---|
1553 | rewrite bits_of_Z_of_bits'. |
---|
1554 | destruct (zlt (n - z') 0). |
---|
1555 | symmetry. apply bits_of_Z_below. omega. |
---|
1556 | destruct (zle (Z_of_nat wordsize) (n - z')). |
---|
1557 | symmetry. apply bits_of_Z_below. omega. |
---|
1558 | decEq. omega. |
---|
1559 | generalize two_wordsize_max_unsigned; omega. |
---|
1560 | apply Z_of_bits_range_2. |
---|
1561 | Qed. |
---|
1562 | |
---|
1563 | Theorem shru_shru: |
---|
1564 | forall x y z, |
---|
1565 | ltu y iwordsize = true -> |
---|
1566 | ltu z iwordsize = true -> |
---|
1567 | ltu (add y z) iwordsize = true -> |
---|
1568 | shru (shru x y) z = shru x (add y z). |
---|
1569 | Proof. |
---|
1570 | intros. unfold shru, add. |
---|
1571 | generalize (ltu_inv _ _ H). |
---|
1572 | generalize (ltu_inv _ _ H0). |
---|
1573 | rewrite unsigned_repr_wordsize. |
---|
1574 | set (x' := unsigned x). |
---|
1575 | set (y' := unsigned y). |
---|
1576 | set (z' := unsigned z). |
---|
1577 | intros. |
---|
1578 | repeat rewrite unsigned_repr. |
---|
1579 | decEq. apply Z_of_bits_exten. intros n R. |
---|
1580 | rewrite bits_of_Z_of_bits'. |
---|
1581 | destruct (zlt (n + z') 0). omegaContradiction. |
---|
1582 | destruct (zle (Z_of_nat wordsize) (n + z')). |
---|
1583 | symmetry. apply bits_of_Z_above. omega. |
---|
1584 | decEq. omega. |
---|
1585 | generalize two_wordsize_max_unsigned; omega. |
---|
1586 | apply Z_of_bits_range_2. |
---|
1587 | Qed. |
---|
1588 | |
---|
1589 | Theorem shru_rolm: |
---|
1590 | forall x n, |
---|
1591 | ltu n iwordsize = true -> |
---|
1592 | shru x n = rolm x (sub iwordsize n) (shru mone n). |
---|
1593 | Proof. |
---|
1594 | intros. generalize (ltu_inv _ _ H). rewrite unsigned_repr_wordsize. intro. |
---|
1595 | unfold shru, rolm, rol, and, bitwise_binop. |
---|
1596 | decEq. apply Z_of_bits_exten; intros. |
---|
1597 | repeat rewrite unsigned_repr; auto with ints. |
---|
1598 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1599 | unfold sub. rewrite unsigned_repr_wordsize. |
---|
1600 | rewrite unsigned_repr. |
---|
1601 | case (zlt (z + unsigned n) (Z_of_nat wordsize)); intro LT2. |
---|
1602 | rewrite unsigned_mone. rewrite bits_of_Z_mone. rewrite andb_b_true. |
---|
1603 | decEq. |
---|
1604 | replace (z - (Z_of_nat wordsize - unsigned n)) |
---|
1605 | with ((z + unsigned n) + (-1) * Z_of_nat wordsize). |
---|
1606 | rewrite Z_mod_plus. symmetry. apply Zmod_small. |
---|
1607 | generalize (unsigned_range n). omega. omega. omega. |
---|
1608 | generalize (unsigned_range n). omega. |
---|
1609 | rewrite (bits_of_Z_above wordsize (unsigned x) _ LT2). |
---|
1610 | rewrite (bits_of_Z_above wordsize (unsigned mone) _ LT2). |
---|
1611 | symmetry. apply andb_b_false. |
---|
1612 | split. omega. apply Zle_trans with (Z_of_nat wordsize). |
---|
1613 | generalize (unsigned_range n); omega. apply wordsize_max_unsigned. |
---|
1614 | Qed. |
---|
1615 | |
---|
1616 | Lemma bitwise_binop_shru: |
---|
1617 | forall f x y n, |
---|
1618 | f false false = false -> |
---|
1619 | bitwise_binop f (shru x n) (shru y n) = shru (bitwise_binop f x y) n. |
---|
1620 | Proof. |
---|
1621 | intros. unfold bitwise_binop, shru. |
---|
1622 | decEq. repeat rewrite unsigned_repr; auto with ints. |
---|
1623 | apply Z_of_bits_exten; intros. |
---|
1624 | case (zlt (z + unsigned n) (Z_of_nat wordsize)); intro. |
---|
1625 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1626 | generalize (unsigned_range n); omega. |
---|
1627 | transitivity false. repeat rewrite bits_of_Z_of_bits; auto. |
---|
1628 | repeat rewrite bits_of_Z_above; auto. |
---|
1629 | rewrite bits_of_Z_above; auto. |
---|
1630 | Qed. |
---|
1631 | |
---|
1632 | Lemma and_shru: |
---|
1633 | forall x y n, |
---|
1634 | and (shru x n) (shru y n) = shru (and x y) n. |
---|
1635 | Proof. |
---|
1636 | unfold and; intros. apply bitwise_binop_shru. reflexivity. |
---|
1637 | Qed. |
---|
1638 | |
---|
1639 | Theorem shr_shr: |
---|
1640 | forall x y z, |
---|
1641 | ltu y iwordsize = true -> |
---|
1642 | ltu z iwordsize = true -> |
---|
1643 | ltu (add y z) iwordsize = true -> |
---|
1644 | shr (shr x y) z = shr x (add y z). |
---|
1645 | Proof. |
---|
1646 | intros. unfold shr, add. |
---|
1647 | generalize (ltu_inv _ _ H). |
---|
1648 | generalize (ltu_inv _ _ H0). |
---|
1649 | rewrite unsigned_repr_wordsize. |
---|
1650 | set (x' := signed x). |
---|
1651 | set (y' := unsigned y). |
---|
1652 | set (z' := unsigned z). |
---|
1653 | intros. |
---|
1654 | rewrite unsigned_repr. |
---|
1655 | rewrite two_p_is_exp. |
---|
1656 | rewrite signed_repr. |
---|
1657 | decEq. apply Zdiv_Zdiv. apply two_p_gt_ZERO. omega. apply two_p_gt_ZERO. omega. |
---|
1658 | apply Zdiv_interval_2. unfold x'; apply signed_range. |
---|
1659 | generalize min_signed_neg; omega. |
---|
1660 | generalize max_signed_pos; omega. |
---|
1661 | apply two_p_gt_ZERO. omega. omega. omega. |
---|
1662 | generalize two_wordsize_max_unsigned; omega. |
---|
1663 | Qed. |
---|
1664 | |
---|
1665 | Theorem rol_zero: |
---|
1666 | forall x, |
---|
1667 | rol x zero = x. |
---|
1668 | Proof. |
---|
1669 | intros. transitivity (repr (unsigned x)). |
---|
1670 | unfold rol. apply eqm_samerepr. eapply eqm_trans. 2: apply Z_of_bits_of_Z. |
---|
1671 | apply eqm_refl2. apply Z_of_bits_exten; intros. decEq. rewrite unsigned_zero. |
---|
1672 | replace (z - 0) with z by omega. apply Zmod_small. auto. |
---|
1673 | apply repr_unsigned. |
---|
1674 | Qed. |
---|
1675 | |
---|
1676 | Lemma bitwise_binop_rol: |
---|
1677 | forall f x y n, |
---|
1678 | bitwise_binop f (rol x n) (rol y n) = rol (bitwise_binop f x y) n. |
---|
1679 | Proof. |
---|
1680 | intros. unfold bitwise_binop, rol. |
---|
1681 | decEq. repeat (rewrite unsigned_repr; auto with ints). |
---|
1682 | apply Z_of_bits_exten; intros. |
---|
1683 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1684 | apply Z_mod_lt. generalize wordsize_pos; omega. |
---|
1685 | Qed. |
---|
1686 | |
---|
1687 | Theorem rol_and: |
---|
1688 | forall x y n, |
---|
1689 | rol (and x y) n = and (rol x n) (rol y n). |
---|
1690 | Proof. |
---|
1691 | intros. symmetry. unfold and. apply bitwise_binop_rol. |
---|
1692 | Qed. |
---|
1693 | |
---|
1694 | Theorem rol_rol: |
---|
1695 | forall x n m, |
---|
1696 | Zdivide (Z_of_nat wordsize) modulus -> |
---|
1697 | rol (rol x n) m = rol x (modu (add n m) iwordsize). |
---|
1698 | Proof. |
---|
1699 | intros. unfold rol. decEq. |
---|
1700 | repeat (rewrite unsigned_repr; auto with ints). |
---|
1701 | apply Z_of_bits_exten; intros. |
---|
1702 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1703 | decEq. unfold modu, add. |
---|
1704 | set (W := Z_of_nat wordsize). |
---|
1705 | set (M := unsigned m); set (N := unsigned n). |
---|
1706 | assert (W > 0). unfold W; generalize wordsize_pos; omega. |
---|
1707 | assert (forall a, eqmod W a (unsigned (repr a))). |
---|
1708 | intros. eapply eqmod_divides. apply eqm_unsigned_repr. assumption. |
---|
1709 | apply eqmod_mod_eq. auto. |
---|
1710 | replace (unsigned iwordsize) with W. |
---|
1711 | apply eqmod_trans with (z - (N + M) mod W). |
---|
1712 | apply eqmod_trans with ((z - M) - N). |
---|
1713 | apply eqmod_sub. apply eqmod_sym. apply eqmod_mod. auto. |
---|
1714 | apply eqmod_refl. |
---|
1715 | replace (z - M - N) with (z - (N + M)). |
---|
1716 | apply eqmod_sub. apply eqmod_refl. apply eqmod_mod. auto. |
---|
1717 | omega. |
---|
1718 | apply eqmod_sub. apply eqmod_refl. |
---|
1719 | eapply eqmod_trans; [idtac|apply H2]. |
---|
1720 | eapply eqmod_trans; [idtac|apply eqmod_mod]. |
---|
1721 | apply eqmod_sym. eapply eqmod_trans; [idtac|apply eqmod_mod]. |
---|
1722 | apply eqmod_sym. apply H2. auto. auto. |
---|
1723 | symmetry. unfold W. apply unsigned_repr_wordsize. |
---|
1724 | apply Z_mod_lt. generalize wordsize_pos; omega. |
---|
1725 | Qed. |
---|
1726 | |
---|
1727 | Theorem rolm_zero: |
---|
1728 | forall x m, |
---|
1729 | rolm x zero m = and x m. |
---|
1730 | Proof. |
---|
1731 | intros. unfold rolm. rewrite rol_zero. auto. |
---|
1732 | Qed. |
---|
1733 | |
---|
1734 | Theorem rolm_rolm: |
---|
1735 | forall x n1 m1 n2 m2, |
---|
1736 | Zdivide (Z_of_nat wordsize) modulus -> |
---|
1737 | rolm (rolm x n1 m1) n2 m2 = |
---|
1738 | rolm x (modu (add n1 n2) iwordsize) |
---|
1739 | (and (rol m1 n2) m2). |
---|
1740 | Proof. |
---|
1741 | intros. |
---|
1742 | unfold rolm. rewrite rol_and. rewrite and_assoc. |
---|
1743 | rewrite rol_rol. reflexivity. auto. |
---|
1744 | Qed. |
---|
1745 | |
---|
1746 | Theorem rol_or: |
---|
1747 | forall x y n, |
---|
1748 | rol (or x y) n = or (rol x n) (rol y n). |
---|
1749 | Proof. |
---|
1750 | intros. symmetry. unfold or. apply bitwise_binop_rol. |
---|
1751 | Qed. |
---|
1752 | |
---|
1753 | Theorem or_rolm: |
---|
1754 | forall x n m1 m2, |
---|
1755 | or (rolm x n m1) (rolm x n m2) = rolm x n (or m1 m2). |
---|
1756 | Proof. |
---|
1757 | intros; unfold rolm. symmetry. apply and_or_distrib. |
---|
1758 | Qed. |
---|
1759 | |
---|
1760 | Theorem ror_rol: |
---|
1761 | forall x y, |
---|
1762 | ltu y iwordsize = true -> |
---|
1763 | ror x y = rol x (sub iwordsize y). |
---|
1764 | Proof. |
---|
1765 | intros. unfold ror, rol, sub. |
---|
1766 | generalize (ltu_inv _ _ H). |
---|
1767 | rewrite unsigned_repr_wordsize. |
---|
1768 | intro. rewrite unsigned_repr. |
---|
1769 | decEq. apply Z_of_bits_exten. intros. decEq. |
---|
1770 | apply eqmod_mod_eq. omega. |
---|
1771 | exists 1. omega. |
---|
1772 | generalize wordsize_pos; generalize wordsize_max_unsigned; omega. |
---|
1773 | Qed. |
---|
1774 | |
---|
1775 | Theorem or_ror: |
---|
1776 | forall x y z, |
---|
1777 | ltu y iwordsize = true -> |
---|
1778 | ltu z iwordsize = true -> |
---|
1779 | add y z = iwordsize -> |
---|
1780 | ror x z = or (shl x y) (shru x z). |
---|
1781 | Proof. |
---|
1782 | intros. |
---|
1783 | generalize (ltu_inv _ _ H). |
---|
1784 | generalize (ltu_inv _ _ H0). |
---|
1785 | rewrite unsigned_repr_wordsize. |
---|
1786 | intros. |
---|
1787 | unfold or, bitwise_binop, shl, shru, ror. |
---|
1788 | set (ux := unsigned x). |
---|
1789 | decEq. apply Z_of_bits_exten. intros i iRANGE. |
---|
1790 | repeat rewrite unsigned_repr. |
---|
1791 | repeat rewrite bits_of_Z_of_bits; auto. |
---|
1792 | assert (y = sub iwordsize z). |
---|
1793 | rewrite <- H1. rewrite add_commut. rewrite sub_add_l. rewrite sub_idem. |
---|
1794 | rewrite add_commut. rewrite add_zero. auto. |
---|
1795 | assert (unsigned y = Z_of_nat wordsize - unsigned z). |
---|
1796 | rewrite H4. unfold sub. rewrite unsigned_repr_wordsize. apply unsigned_repr. |
---|
1797 | generalize wordsize_max_unsigned; omega. |
---|
1798 | destruct (zlt (i + unsigned z) (Z_of_nat wordsize)). |
---|
1799 | rewrite Zmod_small. |
---|
1800 | replace (bits_of_Z wordsize ux (i - unsigned y)) with false. |
---|
1801 | auto. |
---|
1802 | symmetry. apply bits_of_Z_below. omega. omega. |
---|
1803 | replace (bits_of_Z wordsize ux (i + unsigned z)) with false. |
---|
1804 | rewrite orb_false_r. decEq. |
---|
1805 | replace (i + unsigned z) with (i - unsigned y + 1 * Z_of_nat wordsize) by omega. |
---|
1806 | rewrite Z_mod_plus. apply Zmod_small. omega. generalize wordsize_pos; omega. |
---|
1807 | symmetry. apply bits_of_Z_above. auto. |
---|
1808 | apply Z_of_bits_range_2. apply Z_of_bits_range_2. |
---|
1809 | Qed. |
---|
1810 | |
---|
1811 | Lemma bits_of_Z_two_p: |
---|
1812 | forall n x i, |
---|
1813 | x >= 0 -> 0 <= i < Z_of_nat n -> |
---|
1814 | bits_of_Z n (two_p x - 1) i = zlt i x. |
---|
1815 | Proof. |
---|
1816 | induction n; intros. |
---|
1817 | simpl in H0. omegaContradiction. |
---|
1818 | destruct (zeq x 0). subst x. change (two_p 0 - 1) with 0. rewrite bits_of_Z_zero. |
---|
1819 | unfold proj_sumbool; rewrite zlt_false. auto. omega. |
---|
1820 | replace (two_p x) with (2 * two_p (x - 1)). simpl. rewrite Z_bin_decomp_2xm1. |
---|
1821 | destruct (zeq i 0). subst. unfold proj_sumbool. rewrite zlt_true. auto. omega. |
---|
1822 | rewrite inj_S in H0. rewrite IHn. unfold proj_sumbool. destruct (zlt i x). |
---|
1823 | apply zlt_true. omega. |
---|
1824 | apply zlt_false. omega. |
---|
1825 | omega. omega. rewrite <- two_p_S. decEq. omega. omega. |
---|
1826 | Qed. |
---|
1827 | |
---|
1828 | Remark two_p_m1_range: |
---|
1829 | forall n, |
---|
1830 | 0 <= n <= Z_of_nat wordsize -> |
---|
1831 | 0 <= two_p n - 1 <= max_unsigned. |
---|
1832 | Proof. |
---|
1833 | intros. split. |
---|
1834 | assert (two_p n > 0). apply two_p_gt_ZERO. omega. omega. |
---|
1835 | assert (two_p n <= two_p (Z_of_nat wordsize)). apply two_p_monotone. auto. |
---|
1836 | unfold max_unsigned. unfold modulus. rewrite two_power_nat_two_p. omega. |
---|
1837 | Qed. |
---|
1838 | |
---|
1839 | Theorem shru_shl_and: |
---|
1840 | forall x y, |
---|
1841 | ltu y iwordsize = true -> |
---|
1842 | shru (shl x y) y = and x (repr (two_p (Z_of_nat wordsize - unsigned y) - 1)). |
---|
1843 | Proof. |
---|
1844 | intros. exploit ltu_inv; eauto. rewrite unsigned_repr_wordsize. intros. |
---|
1845 | unfold and, bitwise_binop, shl, shru. |
---|
1846 | decEq. apply Z_of_bits_exten. intros. |
---|
1847 | repeat rewrite unsigned_repr. |
---|
1848 | rewrite bits_of_Z_two_p. |
---|
1849 | destruct (zlt (z + unsigned y) (Z_of_nat wordsize)). |
---|
1850 | rewrite bits_of_Z_of_bits. unfold proj_sumbool. rewrite zlt_true. |
---|
1851 | rewrite andb_true_r. f_equal. omega. |
---|
1852 | omega. omega. |
---|
1853 | rewrite bits_of_Z_above. unfold proj_sumbool. rewrite zlt_false. rewrite andb_false_r; auto. |
---|
1854 | omega. omega. omega. auto. |
---|
1855 | apply two_p_m1_range. omega. |
---|
1856 | apply Z_of_bits_range_2. |
---|
1857 | Qed. |
---|
1858 | |
---|
1859 | (** ** Relation between shifts and powers of 2 *) |
---|
1860 | |
---|
1861 | Fixpoint powerserie (l: list Z): Z := |
---|
1862 | match l with |
---|
1863 | | nil => 0 |
---|
1864 | | x :: xs => two_p x + powerserie xs |
---|
1865 | end. |
---|
1866 | |
---|
1867 | Lemma Z_bin_decomp_range: |
---|
1868 | forall x n, |
---|
1869 | 0 <= x < 2 * n -> 0 <= snd (Z_bin_decomp x) < n. |
---|
1870 | Proof. |
---|
1871 | intros. rewrite <- (Z_shift_add_bin_decomp x) in H. |
---|
1872 | unfold Z_shift_add in H. destruct (fst (Z_bin_decomp x)); omega. |
---|
1873 | Qed. |
---|
1874 | |
---|
1875 | Lemma Z_one_bits_powerserie: |
---|
1876 | forall x, 0 <= x < modulus -> x = powerserie (Z_one_bits wordsize x 0). |
---|
1877 | Proof. |
---|
1878 | assert (forall n x i, |
---|
1879 | 0 <= i -> |
---|
1880 | 0 <= x < two_power_nat n -> |
---|
1881 | x * two_p i = powerserie (Z_one_bits n x i)). |
---|
1882 | induction n; intros. |
---|
1883 | simpl. rewrite two_power_nat_O in H0. |
---|
1884 | assert (x = 0). omega. subst x. omega. |
---|
1885 | rewrite two_power_nat_S in H0. simpl Z_one_bits. |
---|
1886 | generalize (Z_shift_add_bin_decomp x). |
---|
1887 | generalize (Z_bin_decomp_range x _ H0). |
---|
1888 | case (Z_bin_decomp x). simpl. intros b y RANGE SHADD. |
---|
1889 | subst x. unfold Z_shift_add. |
---|
1890 | destruct b. simpl powerserie. rewrite <- IHn. |
---|
1891 | rewrite two_p_is_exp. change (two_p 1) with 2. ring. |
---|
1892 | auto. omega. omega. auto. |
---|
1893 | rewrite <- IHn. |
---|
1894 | rewrite two_p_is_exp. change (two_p 1) with 2. ring. |
---|
1895 | auto. omega. omega. auto. |
---|
1896 | intros. rewrite <- H. change (two_p 0) with 1. omega. |
---|
1897 | omega. exact H0. |
---|
1898 | Qed. |
---|
1899 | |
---|
1900 | Lemma Z_one_bits_range: |
---|
1901 | forall x i, In i (Z_one_bits wordsize x 0) -> 0 <= i < Z_of_nat wordsize. |
---|
1902 | Proof. |
---|
1903 | assert (forall n x i j, |
---|
1904 | In j (Z_one_bits n x i) -> i <= j < i + Z_of_nat n). |
---|
1905 | induction n; simpl In. |
---|
1906 | intros; elim H. |
---|
1907 | intros x i j. destruct (Z_bin_decomp x). case b. |
---|
1908 | rewrite inj_S. simpl. intros [A|B]. subst j. omega. |
---|
1909 | generalize (IHn _ _ _ B). omega. |
---|
1910 | intros B. rewrite inj_S. generalize (IHn _ _ _ B). omega. |
---|
1911 | intros. generalize (H wordsize x 0 i H0). omega. |
---|
1912 | Qed. |
---|
1913 | |
---|
1914 | Lemma is_power2_rng: |
---|
1915 | forall n logn, |
---|
1916 | is_power2 n = Some logn -> |
---|
1917 | 0 <= unsigned logn < Z_of_nat wordsize. |
---|
1918 | Proof. |
---|
1919 | intros n logn. unfold is_power2. |
---|
1920 | generalize (Z_one_bits_range (unsigned n)). |
---|
1921 | destruct (Z_one_bits wordsize (unsigned n) 0). |
---|
1922 | intros; discriminate. |
---|
1923 | destruct l. |
---|
1924 | intros. injection H0; intro; subst logn; clear H0. |
---|
1925 | assert (0 <= z < Z_of_nat wordsize). |
---|
1926 | apply H. auto with coqlib. |
---|
1927 | rewrite unsigned_repr. auto. generalize wordsize_max_unsigned; omega. |
---|
1928 | intros; discriminate. |
---|
1929 | Qed. |
---|
1930 | |
---|
1931 | Theorem is_power2_range: |
---|
1932 | forall n logn, |
---|
1933 | is_power2 n = Some logn -> ltu logn iwordsize = true. |
---|
1934 | Proof. |
---|
1935 | intros. unfold ltu. rewrite unsigned_repr_wordsize. |
---|
1936 | generalize (is_power2_rng _ _ H). |
---|
1937 | case (zlt (unsigned logn) (Z_of_nat wordsize)); intros. |
---|
1938 | auto. omegaContradiction. |
---|
1939 | Qed. |
---|
1940 | |
---|
1941 | Lemma is_power2_correct: |
---|
1942 | forall n logn, |
---|
1943 | is_power2 n = Some logn -> |
---|
1944 | unsigned n = two_p (unsigned logn). |
---|
1945 | Proof. |
---|
1946 | intros n logn. unfold is_power2. |
---|
1947 | generalize (Z_one_bits_powerserie (unsigned n) (unsigned_range n)). |
---|
1948 | generalize (Z_one_bits_range (unsigned n)). |
---|
1949 | destruct (Z_one_bits wordsize (unsigned n) 0). |
---|
1950 | intros; discriminate. |
---|
1951 | destruct l. |
---|
1952 | intros. simpl in H0. injection H1; intros; subst logn; clear H1. |
---|
1953 | rewrite unsigned_repr. replace (two_p z) with (two_p z + 0). |
---|
1954 | auto. omega. elim (H z); intros. |
---|
1955 | generalize wordsize_max_unsigned; omega. |
---|
1956 | auto with coqlib. |
---|
1957 | intros; discriminate. |
---|
1958 | Qed. |
---|
1959 | |
---|
1960 | Remark two_p_range: |
---|
1961 | forall n, |
---|
1962 | 0 <= n < Z_of_nat wordsize -> |
---|
1963 | 0 <= two_p n <= max_unsigned. |
---|
1964 | Proof. |
---|
1965 | intros. split. |
---|
1966 | assert (two_p n > 0). apply two_p_gt_ZERO. omega. omega. |
---|
1967 | generalize (two_p_monotone_strict _ _ H). rewrite <- two_power_nat_two_p. |
---|
1968 | unfold max_unsigned, modulus. omega. |
---|
1969 | Qed. |
---|
1970 | |
---|
1971 | Remark Z_one_bits_zero: |
---|
1972 | forall n i, Z_one_bits n 0 i = nil. |
---|
1973 | Proof. |
---|
1974 | induction n; intros; simpl; auto. |
---|
1975 | Qed. |
---|
1976 | |
---|
1977 | Remark Z_one_bits_two_p: |
---|
1978 | forall n x i, |
---|
1979 | 0 <= x < Z_of_nat n -> |
---|
1980 | Z_one_bits n (two_p x) i = (i + x) :: nil. |
---|
1981 | Proof. |
---|
1982 | induction n; intros; simpl. simpl in H. omegaContradiction. |
---|
1983 | rewrite inj_S in H. |
---|
1984 | assert (x = 0 \/ 0 < x) by omega. destruct H0. |
---|
1985 | subst x; simpl. decEq. omega. apply Z_one_bits_zero. |
---|
1986 | replace (two_p x) with (Z_shift_add false (two_p (x-1))). |
---|
1987 | rewrite Z_bin_decomp_shift_add. |
---|
1988 | replace (i + x) with ((i + 1) + (x - 1)) by omega. |
---|
1989 | apply IHn. omega. |
---|
1990 | unfold Z_shift_add. rewrite <- two_p_S. decEq; omega. omega. |
---|
1991 | Qed. |
---|
1992 | |
---|
1993 | Lemma is_power2_two_p: |
---|
1994 | forall n, 0 <= n < Z_of_nat wordsize -> |
---|
1995 | is_power2 (repr (two_p n)) = Some (repr n). |
---|
1996 | Proof. |
---|
1997 | intros. unfold is_power2. rewrite unsigned_repr. |
---|
1998 | rewrite Z_one_bits_two_p. auto. auto. |
---|
1999 | apply two_p_range. auto. |
---|
2000 | Qed. |
---|
2001 | |
---|
2002 | Theorem mul_pow2: |
---|
2003 | forall x n logn, |
---|
2004 | is_power2 n = Some logn -> |
---|
2005 | mul x n = shl x logn. |
---|
2006 | Proof. |
---|
2007 | intros. generalize (is_power2_correct n logn H); intro. |
---|
2008 | rewrite shl_mul_two_p. rewrite <- H0. rewrite repr_unsigned. |
---|
2009 | auto. |
---|
2010 | Qed. |
---|
2011 | |
---|
2012 | Lemma Z_of_bits_shift_rev: |
---|
2013 | forall n f, |
---|
2014 | (forall i, i >= Z_of_nat n -> f i = false) -> |
---|
2015 | Z_of_bits n f = Z_shift_add (f 0) (Z_of_bits n (fun i => f(i + 1))). |
---|
2016 | Proof. |
---|
2017 | induction n; intros. |
---|
2018 | simpl. rewrite H. reflexivity. unfold Z_of_nat. omega. |
---|
2019 | simpl. rewrite (IHn (fun i => f (i + 1))). |
---|
2020 | reflexivity. |
---|
2021 | intros. apply H. rewrite inj_S. omega. |
---|
2022 | Qed. |
---|
2023 | |
---|
2024 | Lemma Z_of_bits_shifts_rev: |
---|
2025 | forall m f, |
---|
2026 | 0 <= m -> |
---|
2027 | (forall i, i >= Z_of_nat wordsize -> f i = false) -> |
---|
2028 | exists k, |
---|
2029 | Z_of_bits wordsize f = k + two_p m * Z_of_bits wordsize (fun i => f(i + m)) |
---|
2030 | /\ 0 <= k < two_p m. |
---|
2031 | Proof. |
---|
2032 | intros. pattern m. apply natlike_ind. |
---|
2033 | exists 0. change (two_p 0) with 1. split. |
---|
2034 | transitivity (Z_of_bits wordsize (fun i => f (i + 0))). |
---|
2035 | apply Z_of_bits_exten. intros. decEq. omega. |
---|
2036 | omega. omega. |
---|
2037 | intros x POSx [k [EQ1 RANGE1]]. |
---|
2038 | set (f' := fun i => f (i + x)) in *. |
---|
2039 | assert (forall i, i >= Z_of_nat wordsize -> f' i = false). |
---|
2040 | intros. unfold f'. apply H0. omega. |
---|
2041 | generalize (Z_of_bits_shift_rev wordsize f' H1). intro. |
---|
2042 | rewrite EQ1. rewrite H2. |
---|
2043 | set (z := Z_of_bits wordsize (fun i => f (i + Zsucc x))). |
---|
2044 | replace (Z_of_bits wordsize (fun i => f' (i + 1))) with z. |
---|
2045 | rewrite two_p_S. |
---|
2046 | case (f' 0); unfold Z_shift_add. |
---|
2047 | exists (k + two_p x). split. ring. omega. |
---|
2048 | exists k. split. ring. omega. |
---|
2049 | auto. |
---|
2050 | unfold z. apply Z_of_bits_exten; intros. unfold f'. |
---|
2051 | decEq. omega. |
---|
2052 | auto. |
---|
2053 | Qed. |
---|
2054 | |
---|
2055 | Lemma shru_div_two_p: |
---|
2056 | forall x y, |
---|
2057 | shru x y = repr (unsigned x / two_p (unsigned y)). |
---|
2058 | Proof. |
---|
2059 | intros. unfold shru. |
---|
2060 | set (x' := unsigned x). set (y' := unsigned y). |
---|
2061 | elim (Z_of_bits_shifts_rev y' (bits_of_Z wordsize x')). |
---|
2062 | intros k [EQ RANGE]. |
---|
2063 | replace (Z_of_bits wordsize (bits_of_Z wordsize x')) with x' in EQ. |
---|
2064 | rewrite Zplus_comm in EQ. rewrite Zmult_comm in EQ. |
---|
2065 | generalize (Zdiv_unique _ _ _ _ EQ RANGE). intros. |
---|
2066 | rewrite H. auto. |
---|
2067 | apply eqm_small_eq. apply eqm_sym. apply Z_of_bits_of_Z. |
---|
2068 | unfold x'. apply unsigned_range. |
---|
2069 | auto with ints. |
---|
2070 | generalize (unsigned_range y). unfold y'. omega. |
---|
2071 | intros. apply bits_of_Z_above. auto. |
---|
2072 | Qed. |
---|
2073 | |
---|
2074 | Theorem shru_zero: |
---|
2075 | forall x, shru x zero = x. |
---|
2076 | Proof. |
---|
2077 | intros. rewrite shru_div_two_p. change (two_p (unsigned zero)) with 1. |
---|
2078 | transitivity (repr (unsigned x)). decEq. apply Zdiv_unique with 0. |
---|
2079 | omega. omega. auto with ints. |
---|
2080 | Qed. |
---|
2081 | |
---|
2082 | Theorem shr_zero: |
---|
2083 | forall x, shr x zero = x. |
---|
2084 | Proof. |
---|
2085 | intros. unfold shr. change (two_p (unsigned zero)) with 1. |
---|
2086 | replace (signed x / 1) with (signed x). |
---|
2087 | apply repr_signed. |
---|
2088 | symmetry. apply Zdiv_unique with 0. omega. omega. |
---|
2089 | Qed. |
---|
2090 | |
---|
2091 | Theorem divu_pow2: |
---|
2092 | forall x n logn, |
---|
2093 | is_power2 n = Some logn -> |
---|
2094 | divu x n = shru x logn. |
---|
2095 | Proof. |
---|
2096 | intros. generalize (is_power2_correct n logn H). intro. |
---|
2097 | symmetry. unfold divu. rewrite H0. apply shru_div_two_p. |
---|
2098 | Qed. |
---|
2099 | |
---|
2100 | Lemma modu_divu_Euclid: |
---|
2101 | forall x y, y <> zero -> x = add (mul (divu x y) y) (modu x y). |
---|
2102 | Proof. |
---|
2103 | intros. unfold add, mul, divu, modu. |
---|
2104 | transitivity (repr (unsigned x)). auto with ints. |
---|
2105 | apply eqm_samerepr. |
---|
2106 | set (x' := unsigned x). set (y' := unsigned y). |
---|
2107 | apply eqm_trans with ((x' / y') * y' + x' mod y'). |
---|
2108 | apply eqm_refl2. rewrite Zmult_comm. apply Z_div_mod_eq. |
---|
2109 | generalize (unsigned_range y); intro. |
---|
2110 | assert (unsigned y <> 0). red; intro. |
---|
2111 | elim H. rewrite <- (repr_unsigned y). unfold zero. congruence. |
---|
2112 | unfold y'. omega. |
---|
2113 | auto with ints. |
---|
2114 | Qed. |
---|
2115 | |
---|
2116 | Theorem modu_divu: |
---|
2117 | forall x y, y <> zero -> modu x y = sub x (mul (divu x y) y). |
---|
2118 | Proof. |
---|
2119 | intros. |
---|
2120 | assert (forall a b c, a = add b c -> c = sub a b). |
---|
2121 | intros. subst a. rewrite sub_add_l. rewrite sub_idem. |
---|
2122 | rewrite add_commut. rewrite add_zero. auto. |
---|
2123 | apply H0. apply modu_divu_Euclid. auto. |
---|
2124 | Qed. |
---|
2125 | |
---|
2126 | Theorem mods_divs: |
---|
2127 | forall x y, mods x y = sub x (mul (divs x y) y). |
---|
2128 | Proof. |
---|
2129 | intros; unfold mods, sub, mul, divs. |
---|
2130 | apply eqm_samerepr. |
---|
2131 | unfold Zmod_round. |
---|
2132 | apply eqm_sub. apply eqm_signed_unsigned. |
---|
2133 | apply eqm_unsigned_repr_r. |
---|
2134 | apply eqm_mult. auto with ints. apply eqm_signed_unsigned. |
---|
2135 | Qed. |
---|
2136 | |
---|
2137 | Theorem divs_pow2: |
---|
2138 | forall x n logn, |
---|
2139 | is_power2 n = Some logn -> |
---|
2140 | divs x n = shrx x logn. |
---|
2141 | Proof. |
---|
2142 | intros. generalize (is_power2_correct _ _ H); intro. |
---|
2143 | unfold shrx. rewrite shl_mul_two_p. |
---|
2144 | rewrite mul_commut. rewrite mul_one. |
---|
2145 | rewrite <- H0. rewrite repr_unsigned. auto. |
---|
2146 | Qed. |
---|
2147 | |
---|
2148 | Theorem shrx_carry: |
---|
2149 | forall x y, |
---|
2150 | add (shr x y) (shr_carry x y) = shrx x y. |
---|
2151 | Proof. |
---|
2152 | intros. unfold shr_carry. |
---|
2153 | rewrite sub_add_opp. rewrite add_permut. |
---|
2154 | rewrite add_neg_zero. apply add_zero. |
---|
2155 | Qed. |
---|
2156 | |
---|
2157 | Lemma Zdiv_round_Zdiv: |
---|
2158 | forall x y, |
---|
2159 | y > 0 -> |
---|
2160 | Zdiv_round x y = if zlt x 0 then (x + y - 1) / y else x / y. |
---|
2161 | Proof. |
---|
2162 | intros. unfold Zdiv_round. |
---|
2163 | destruct (zlt x 0). |
---|
2164 | rewrite zlt_false; try omega. |
---|
2165 | generalize (Z_div_mod_eq (-x) y H). |
---|
2166 | generalize (Z_mod_lt (-x) y H). |
---|
2167 | set (q := (-x) / y). set (r := (-x) mod y). intros. |
---|
2168 | symmetry. |
---|
2169 | apply Zdiv_unique with (y - r - 1). |
---|
2170 | replace x with (- (y * q) - r) by omega. |
---|
2171 | replace (-(y * q)) with ((-q) * y) by ring. |
---|
2172 | omega. |
---|
2173 | omega. |
---|
2174 | apply zlt_false. omega. |
---|
2175 | Qed. |
---|
2176 | |
---|
2177 | Theorem shrx_shr: |
---|
2178 | forall x y, |
---|
2179 | ltu y (repr (Z_of_nat wordsize - 1)) = true -> |
---|
2180 | shrx x y = |
---|
2181 | shr (if lt x zero then add x (sub (shl one y) one) else x) y. |
---|
2182 | Proof. |
---|
2183 | intros. unfold shrx, divs, shr. decEq. |
---|
2184 | exploit ltu_inv; eauto. rewrite unsigned_repr. |
---|
2185 | set (uy := unsigned y). |
---|
2186 | intro RANGE. |
---|
2187 | assert (shl one y = repr (two_p uy)). |
---|
2188 | transitivity (mul one (repr (two_p uy))). |
---|
2189 | symmetry. apply mul_pow2. replace y with (repr uy). |
---|
2190 | apply is_power2_two_p. omega. unfold uy. apply repr_unsigned. |
---|
2191 | rewrite mul_commut. apply mul_one. |
---|
2192 | assert (two_p uy > 0). apply two_p_gt_ZERO. omega. |
---|
2193 | assert (two_p uy < half_modulus). |
---|
2194 | rewrite half_modulus_power. |
---|
2195 | apply two_p_monotone_strict. auto. |
---|
2196 | assert (two_p uy < modulus). |
---|
2197 | rewrite modulus_power. apply two_p_monotone_strict. omega. |
---|
2198 | assert (unsigned (shl one y) = two_p uy). |
---|
2199 | rewrite H0. apply unsigned_repr. unfold max_unsigned. omega. |
---|
2200 | assert (signed (shl one y) = two_p uy). |
---|
2201 | rewrite H0. apply signed_repr. |
---|
2202 | unfold max_signed. generalize min_signed_neg. omega. |
---|
2203 | rewrite H5. |
---|
2204 | rewrite Zdiv_round_Zdiv; auto. |
---|
2205 | unfold lt. rewrite signed_zero. |
---|
2206 | destruct (zlt (signed x) 0); auto. |
---|
2207 | rewrite add_signed. |
---|
2208 | assert (signed (sub (shl one y) one) = two_p uy - 1). |
---|
2209 | unfold sub. rewrite H4. rewrite unsigned_one. |
---|
2210 | apply signed_repr. |
---|
2211 | generalize min_signed_neg. unfold max_signed. omega. |
---|
2212 | rewrite H6. rewrite signed_repr. decEq. omega. |
---|
2213 | generalize (signed_range x). intros. |
---|
2214 | assert (two_p uy - 1 <= max_signed). unfold max_signed. omega. |
---|
2215 | omega. |
---|
2216 | generalize wordsize_pos wordsize_max_unsigned; omega. |
---|
2217 | Qed. |
---|
2218 | |
---|
2219 | Lemma add_and: |
---|
2220 | forall x y z, |
---|
2221 | and y z = zero -> |
---|
2222 | add (and x y) (and x z) = and x (or y z). |
---|
2223 | Proof. |
---|
2224 | intros. unfold add, and, bitwise_binop. |
---|
2225 | decEq. |
---|
2226 | repeat rewrite unsigned_repr; auto with ints. |
---|
2227 | apply Z_of_bits_excl; intros. |
---|
2228 | assert (forall a b c, a && b && (a && c) = a && (b && c)). |
---|
2229 | destruct a; destruct b; destruct c; reflexivity. |
---|
2230 | rewrite H1. |
---|
2231 | replace (bits_of_Z wordsize (unsigned y) i && |
---|
2232 | bits_of_Z wordsize (unsigned z) i) |
---|
2233 | with (bits_of_Z wordsize (unsigned (and y z)) i). |
---|
2234 | rewrite H. change (unsigned zero) with 0. |
---|
2235 | rewrite bits_of_Z_zero. apply andb_b_false. |
---|
2236 | unfold and, bitwise_binop. |
---|
2237 | rewrite unsigned_repr; auto with ints. rewrite bits_of_Z_of_bits. |
---|
2238 | reflexivity. auto. |
---|
2239 | rewrite <- demorgan1. |
---|
2240 | unfold or, bitwise_binop. |
---|
2241 | rewrite unsigned_repr; auto with ints. rewrite bits_of_Z_of_bits; auto. |
---|
2242 | Qed. |
---|
2243 | |
---|
2244 | Lemma Z_of_bits_zero: |
---|
2245 | forall n f, |
---|
2246 | (forall i, i >= 0 -> f i = false) -> |
---|
2247 | Z_of_bits n f = 0. |
---|
2248 | Proof. |
---|
2249 | induction n; intros; simpl. |
---|
2250 | auto. |
---|
2251 | rewrite H. rewrite IHn. auto. intros. apply H. omega. omega. |
---|
2252 | Qed. |
---|
2253 | |
---|
2254 | Lemma Z_of_bits_trunc_1: |
---|
2255 | forall n f k, |
---|
2256 | (forall i, i >= k -> f i = false) -> |
---|
2257 | k >= 0 -> |
---|
2258 | 0 <= Z_of_bits n f < two_p k. |
---|
2259 | Proof. |
---|
2260 | induction n; intros. |
---|
2261 | simpl. assert (two_p k > 0). apply two_p_gt_ZERO; omega. omega. |
---|
2262 | destruct (zeq k 0). subst k. |
---|
2263 | change (two_p 0) with 1. rewrite Z_of_bits_zero. omega. auto. |
---|
2264 | simpl. replace (two_p k) with (2 * two_p (k - 1)). |
---|
2265 | assert (0 <= Z_of_bits n (fun i => f(i+1)) < two_p (k - 1)). |
---|
2266 | apply IHn. intros. apply H. omega. omega. |
---|
2267 | unfold Z_shift_add. destruct (f 0); omega. |
---|
2268 | rewrite <- two_p_S. decEq. omega. omega. |
---|
2269 | Qed. |
---|
2270 | |
---|
2271 | Lemma Z_of_bits_trunc_2: |
---|
2272 | forall n f1 f2 k, |
---|
2273 | (forall i, i < k -> f2 i = f1 i) -> |
---|
2274 | k >= 0 -> |
---|
2275 | exists q, Z_of_bits n f1 = q * two_p k + Z_of_bits n f2. |
---|
2276 | Proof. |
---|
2277 | induction n; intros. |
---|
2278 | simpl. exists 0; omega. |
---|
2279 | destruct (zeq k 0). subst k. |
---|
2280 | exists (Z_of_bits (S n) f1 - Z_of_bits (S n) f2). |
---|
2281 | change (two_p 0) with 1. omega. |
---|
2282 | destruct (IHn (fun i => f1 (i + 1)) (fun i => f2 (i + 1)) (k - 1)) as [q EQ]. |
---|
2283 | intros. apply H. omega. omega. |
---|
2284 | exists q. simpl. rewrite H. unfold Z_shift_add. |
---|
2285 | replace (two_p k) with (2 * two_p (k - 1)). rewrite EQ. |
---|
2286 | destruct (f1 0). ring. ring. |
---|
2287 | rewrite <- two_p_S. decEq. omega. omega. omega. |
---|
2288 | Qed. |
---|
2289 | |
---|
2290 | Lemma Z_of_bits_trunc_3: |
---|
2291 | forall f n k, |
---|
2292 | k >= 0 -> |
---|
2293 | Zmod (Z_of_bits n f) (two_p k) = Z_of_bits n (fun i => if zlt i k then f i else false). |
---|
2294 | Proof. |
---|
2295 | intros. |
---|
2296 | set (g := fun i : Z => if zlt i k then f i else false). |
---|
2297 | destruct (Z_of_bits_trunc_2 n f g k). |
---|
2298 | intros. unfold g. apply zlt_true. auto. |
---|
2299 | auto. |
---|
2300 | apply Zmod_unique with x. auto. |
---|
2301 | apply Z_of_bits_trunc_1. intros. unfold g. apply zlt_false. auto. auto. |
---|
2302 | Qed. |
---|
2303 | |
---|
2304 | Theorem modu_and: |
---|
2305 | forall x n logn, |
---|
2306 | is_power2 n = Some logn -> |
---|
2307 | modu x n = and x (sub n one). |
---|
2308 | Proof. |
---|
2309 | intros. generalize (is_power2_correct _ _ H); intro. |
---|
2310 | generalize (is_power2_rng _ _ H); intro. |
---|
2311 | unfold modu, and, bitwise_binop. |
---|
2312 | decEq. |
---|
2313 | set (ux := unsigned x). |
---|
2314 | replace ux with (Z_of_bits wordsize (bits_of_Z wordsize ux)). |
---|
2315 | rewrite H0. rewrite Z_of_bits_trunc_3. apply Z_of_bits_exten. intros. |
---|
2316 | rewrite bits_of_Z_of_bits; auto. |
---|
2317 | replace (unsigned (sub n one)) with (two_p (unsigned logn) - 1). |
---|
2318 | rewrite bits_of_Z_two_p. unfold proj_sumbool. |
---|
2319 | destruct (zlt z (unsigned logn)). rewrite andb_true_r; auto. rewrite andb_false_r; auto. |
---|
2320 | omega. auto. |
---|
2321 | rewrite <- H0. unfold sub. symmetry. rewrite unsigned_one. apply unsigned_repr. |
---|
2322 | rewrite H0. |
---|
2323 | assert (two_p (unsigned logn) > 0). apply two_p_gt_ZERO. omega. |
---|
2324 | generalize (two_p_range _ H1). omega. |
---|
2325 | omega. |
---|
2326 | apply eqm_small_eq. apply Z_of_bits_of_Z. apply Z_of_bits_range. |
---|
2327 | unfold ux. apply unsigned_range. |
---|
2328 | Qed. |
---|
2329 | |
---|
2330 | (** ** Properties of integer zero extension and sign extension. *) |
---|
2331 | |
---|
2332 | Section EXTENSIONS. |
---|
2333 | |
---|
2334 | Variable n: Z. |
---|
2335 | Hypothesis RANGE: 0 < n < Z_of_nat wordsize. |
---|
2336 | |
---|
2337 | Remark two_p_n_pos: |
---|
2338 | two_p n > 0. |
---|
2339 | Proof. apply two_p_gt_ZERO. omega. Qed. |
---|
2340 | |
---|
2341 | Remark two_p_n_range: |
---|
2342 | 0 <= two_p n <= max_unsigned. |
---|
2343 | Proof. apply two_p_range. omega. Qed. |
---|
2344 | |
---|
2345 | Remark two_p_n_range': |
---|
2346 | two_p n <= max_signed + 1. |
---|
2347 | Proof. |
---|
2348 | unfold max_signed. rewrite half_modulus_power. |
---|
2349 | assert (two_p n <= two_p (Z_of_nat wordsize - 1)). |
---|
2350 | apply two_p_monotone. omega. |
---|
2351 | omega. |
---|
2352 | Qed. |
---|
2353 | |
---|
2354 | Remark unsigned_repr_two_p: |
---|
2355 | unsigned (repr (two_p n)) = two_p n. |
---|
2356 | Proof. |
---|
2357 | apply unsigned_repr. apply two_p_n_range. |
---|
2358 | Qed. |
---|
2359 | |
---|
2360 | Theorem zero_ext_and: |
---|
2361 | forall x, zero_ext n x = and x (repr (two_p n - 1)). |
---|
2362 | Proof. |
---|
2363 | intros; unfold zero_ext. |
---|
2364 | assert (is_power2 (repr (two_p n)) = Some (repr n)). |
---|
2365 | apply is_power2_two_p. omega. |
---|
2366 | generalize (modu_and x _ _ H). |
---|
2367 | unfold modu. rewrite unsigned_repr_two_p. intro. rewrite H0. |
---|
2368 | decEq. unfold sub. decEq. rewrite unsigned_repr_two_p. |
---|
2369 | rewrite unsigned_one. reflexivity. |
---|
2370 | Qed. |
---|
2371 | |
---|
2372 | Theorem zero_ext_idem: |
---|
2373 | forall x, zero_ext n (zero_ext n x) = zero_ext n x. |
---|
2374 | Proof. |
---|
2375 | intros. repeat rewrite zero_ext_and. |
---|
2376 | rewrite and_assoc. rewrite and_idem. auto. |
---|
2377 | Qed. |
---|
2378 | |
---|
2379 | Lemma eqm_eqmod_two_p: |
---|
2380 | forall a b, eqm a b -> eqmod (two_p n) a b. |
---|
2381 | Proof. |
---|
2382 | intros a b [k EQ]. |
---|
2383 | exists (k * two_p (Z_of_nat wordsize - n)). |
---|
2384 | rewrite EQ. decEq. rewrite <- Zmult_assoc. decEq. |
---|
2385 | rewrite <- two_p_is_exp. unfold modulus. rewrite two_power_nat_two_p. |
---|
2386 | decEq. omega. omega. omega. |
---|
2387 | Qed. |
---|
2388 | |
---|
2389 | Lemma sign_ext_charact: |
---|
2390 | forall x y, |
---|
2391 | -(two_p (n-1)) <= signed y < two_p (n-1) -> |
---|
2392 | eqmod (two_p n) (unsigned x) (signed y) -> |
---|
2393 | sign_ext n x = y. |
---|
2394 | Proof. |
---|
2395 | intros. unfold sign_ext. set (x' := unsigned x) in *. |
---|
2396 | destruct H0 as [k EQ]. |
---|
2397 | assert (two_p n = 2 * two_p (n - 1)). rewrite <- two_p_S. decEq. omega. omega. |
---|
2398 | assert (signed y >= 0 \/ signed y < 0) by omega. destruct H1. |
---|
2399 | assert (x' mod two_p n = signed y). |
---|
2400 | apply Zmod_unique with k; auto. omega. |
---|
2401 | rewrite zlt_true. rewrite H2. apply repr_signed. omega. |
---|
2402 | assert (x' mod two_p n = signed y + two_p n). |
---|
2403 | apply Zmod_unique with (k-1). rewrite EQ. ring. omega. |
---|
2404 | rewrite zlt_false. replace (x' mod two_p n - two_p n) with (signed y) by omega. apply repr_signed. |
---|
2405 | omega. |
---|
2406 | Qed. |
---|
2407 | |
---|
2408 | Lemma zero_ext_eqmod_two_p: |
---|
2409 | forall x y, |
---|
2410 | eqmod (two_p n) (unsigned x) (unsigned y) -> zero_ext n x = zero_ext n y. |
---|
2411 | Proof. |
---|
2412 | intros. unfold zero_ext. decEq. apply eqmod_mod_eq. apply two_p_n_pos. auto. |
---|
2413 | Qed. |
---|
2414 | |
---|
2415 | Lemma sign_ext_eqmod_two_p: |
---|
2416 | forall x y, |
---|
2417 | eqmod (two_p n) (unsigned x) (unsigned y) -> sign_ext n x = sign_ext n y. |
---|
2418 | Proof. |
---|
2419 | intros. unfold sign_ext. |
---|
2420 | assert (unsigned x mod two_p n = unsigned y mod two_p n). |
---|
2421 | apply eqmod_mod_eq. apply two_p_n_pos. auto. |
---|
2422 | rewrite H0. auto. |
---|
2423 | Qed. |
---|
2424 | |
---|
2425 | Lemma eqmod_two_p_zero_ext: |
---|
2426 | forall x, eqmod (two_p n) (unsigned x) (unsigned (zero_ext n x)). |
---|
2427 | Proof. |
---|
2428 | intros. unfold zero_ext. |
---|
2429 | apply eqmod_trans with (unsigned x mod two_p n). |
---|
2430 | apply eqmod_mod. apply two_p_n_pos. |
---|
2431 | apply eqm_eqmod_two_p. apply eqm_unsigned_repr. |
---|
2432 | Qed. |
---|
2433 | |
---|
2434 | Lemma eqmod_two_p_sign_ext: |
---|
2435 | forall x, eqmod (two_p n) (unsigned x) (unsigned (sign_ext n x)). |
---|
2436 | Proof. |
---|
2437 | intros. unfold sign_ext. destruct (zlt (unsigned x mod two_p n) (two_p (n-1))). |
---|
2438 | apply eqmod_trans with (unsigned x mod two_p n). |
---|
2439 | apply eqmod_mod. apply two_p_n_pos. |
---|
2440 | apply eqm_eqmod_two_p. apply eqm_unsigned_repr. |
---|
2441 | apply eqmod_trans with (unsigned x mod two_p n). |
---|
2442 | apply eqmod_mod. apply two_p_n_pos. |
---|
2443 | apply eqmod_trans with (unsigned x mod two_p n - 0). |
---|
2444 | apply eqmod_refl2. omega. |
---|
2445 | apply eqmod_trans with (unsigned x mod two_p n - two_p n). |
---|
2446 | apply eqmod_sub. apply eqmod_refl. exists (-1). ring. |
---|
2447 | apply eqm_eqmod_two_p. apply eqm_unsigned_repr. |
---|
2448 | Qed. |
---|
2449 | |
---|
2450 | Theorem sign_ext_idem: |
---|
2451 | forall x, sign_ext n (sign_ext n x) = sign_ext n x. |
---|
2452 | Proof. |
---|
2453 | intros. apply sign_ext_eqmod_two_p. |
---|
2454 | apply eqmod_sym. apply eqmod_two_p_sign_ext. |
---|
2455 | Qed. |
---|
2456 | *) |
---|
2457 | axiom sign_ext_zero_ext: |
---|
2458 | ∀n:Z.∀RANGE: 0 < n ∧ n < wordsize.∀x. sign_ext n (zero_ext n x) = sign_ext n x. |
---|
2459 | (* |
---|
2460 | Theorem sign_ext_zero_ext: |
---|
2461 | forall x, sign_ext n (zero_ext n x) = sign_ext n x. |
---|
2462 | Proof. |
---|
2463 | intros. apply sign_ext_eqmod_two_p. |
---|
2464 | apply eqmod_sym. apply eqmod_two_p_zero_ext. |
---|
2465 | Qed. |
---|
2466 | |
---|
2467 | Theorem zero_ext_sign_ext: |
---|
2468 | forall x, zero_ext n (sign_ext n x) = zero_ext n x. |
---|
2469 | Proof. |
---|
2470 | intros. apply zero_ext_eqmod_two_p. |
---|
2471 | apply eqmod_sym. apply eqmod_two_p_sign_ext. |
---|
2472 | Qed. |
---|
2473 | *) |
---|
2474 | axiom sign_ext_equal_if_zero_equal: |
---|
2475 | ∀n:Z.∀RANGE: 0 < n ∧ n < wordsize.∀x,y. |
---|
2476 | zero_ext n x = zero_ext n y -> |
---|
2477 | sign_ext n x = sign_ext n y. |
---|
2478 | (* |
---|
2479 | Theorem sign_ext_equal_if_zero_equal: |
---|
2480 | forall x y, |
---|
2481 | zero_ext n x = zero_ext n y -> |
---|
2482 | sign_ext n x = sign_ext n y. |
---|
2483 | Proof. |
---|
2484 | intros. rewrite <- (sign_ext_zero_ext x). |
---|
2485 | rewrite <- (sign_ext_zero_ext y). congruence. |
---|
2486 | Qed. |
---|
2487 | |
---|
2488 | Lemma eqmod_mult_div: |
---|
2489 | forall n1 n2 x y, |
---|
2490 | 0 <= n1 -> 0 <= n2 -> |
---|
2491 | eqmod (two_p (n1+n2)) (two_p n1 * x) y -> |
---|
2492 | eqmod (two_p n2) x (y / two_p n1). |
---|
2493 | Proof. |
---|
2494 | intros. rewrite two_p_is_exp in H1; auto. |
---|
2495 | destruct H1 as [k EQ]. exists k. |
---|
2496 | change x with (0 / two_p n1 + x). rewrite <- Z_div_plus. |
---|
2497 | replace (0 + x * two_p n1) with (two_p n1 * x) by ring. |
---|
2498 | rewrite EQ. |
---|
2499 | replace (k * (two_p n1 * two_p n2) + y) with (y + (k * two_p n2) * two_p n1) by ring. |
---|
2500 | rewrite Z_div_plus. ring. |
---|
2501 | apply two_p_gt_ZERO; auto. |
---|
2502 | apply two_p_gt_ZERO; auto. |
---|
2503 | Qed. |
---|
2504 | |
---|
2505 | Theorem sign_ext_shr_shl: |
---|
2506 | forall x, |
---|
2507 | let y := repr (Z_of_nat wordsize - n) in |
---|
2508 | sign_ext n x = shr (shl x y) y. |
---|
2509 | Proof. |
---|
2510 | intros. |
---|
2511 | assert (unsigned y = Z_of_nat wordsize - n). |
---|
2512 | unfold y. apply unsigned_repr. generalize wordsize_max_unsigned. omega. |
---|
2513 | apply sign_ext_charact. |
---|
2514 | (* inequalities *) |
---|
2515 | unfold shr. rewrite H. |
---|
2516 | set (z := signed (shl x y)). |
---|
2517 | rewrite signed_repr. |
---|
2518 | apply Zdiv_interval_1. |
---|
2519 | assert (two_p (n - 1) > 0). apply two_p_gt_ZERO. omega. omega. |
---|
2520 | apply two_p_gt_ZERO. omega. |
---|
2521 | apply two_p_gt_ZERO. omega. |
---|
2522 | replace ((- two_p (n-1)) * two_p (Z_of_nat wordsize - n)) |
---|
2523 | with (- (two_p (n-1) * two_p (Z_of_nat wordsize - n))) by ring. |
---|
2524 | rewrite <- two_p_is_exp. |
---|
2525 | replace (n - 1 + (Z_of_nat wordsize - n)) with (Z_of_nat wordsize - 1) by omega. |
---|
2526 | rewrite <- half_modulus_power. |
---|
2527 | generalize (signed_range (shl x y)). unfold z, min_signed, max_signed. omega. |
---|
2528 | omega. omega. |
---|
2529 | apply Zdiv_interval_2. unfold z. apply signed_range. |
---|
2530 | generalize min_signed_neg; omega. generalize max_signed_pos; omega. |
---|
2531 | apply two_p_gt_ZERO; omega. |
---|
2532 | (* eqmod *) |
---|
2533 | unfold shr. rewrite H. |
---|
2534 | apply eqmod_trans with (signed (shl x y) / two_p (Z_of_nat wordsize - n)). |
---|
2535 | apply eqmod_mult_div. omega. omega. |
---|
2536 | replace (Z_of_nat wordsize - n + n) with (Z_of_nat wordsize) by omega. |
---|
2537 | rewrite <- two_power_nat_two_p. |
---|
2538 | change (eqm (two_p (Z_of_nat wordsize - n) * unsigned x) (signed (shl x y))). |
---|
2539 | rewrite shl_mul_two_p. unfold mul. rewrite H. |
---|
2540 | apply eqm_sym. eapply eqm_trans. apply eqm_signed_unsigned. |
---|
2541 | apply eqm_unsigned_repr_l. rewrite (Zmult_comm (unsigned x)). |
---|
2542 | apply eqm_mult. apply eqm_sym. apply eqm_unsigned_repr. apply eqm_refl. |
---|
2543 | apply eqm_eqmod_two_p. apply eqm_sym. eapply eqm_trans. |
---|
2544 | apply eqm_signed_unsigned. apply eqm_sym. apply eqm_unsigned_repr. |
---|
2545 | Qed. |
---|
2546 | |
---|
2547 | Theorem zero_ext_shru_shl: |
---|
2548 | forall x, |
---|
2549 | let y := repr (Z_of_nat wordsize - n) in |
---|
2550 | zero_ext n x = shru (shl x y) y. |
---|
2551 | Proof. |
---|
2552 | intros. |
---|
2553 | assert (unsigned y = Z_of_nat wordsize - n). |
---|
2554 | unfold y. apply unsigned_repr. generalize wordsize_max_unsigned. omega. |
---|
2555 | rewrite zero_ext_and. symmetry. |
---|
2556 | replace n with (Z_of_nat wordsize - unsigned y). |
---|
2557 | apply shru_shl_and. unfold ltu. apply zlt_true. |
---|
2558 | rewrite H. rewrite unsigned_repr_wordsize. omega. omega. |
---|
2559 | Qed. |
---|
2560 | |
---|
2561 | End EXTENSIONS. |
---|
2562 | |
---|
2563 | (** ** Properties of [one_bits] (decomposition in sum of powers of two) *) |
---|
2564 | |
---|
2565 | Opaque Z_one_bits. (* Otherwise, next Qed blows up! *) |
---|
2566 | |
---|
2567 | Theorem one_bits_range: |
---|
2568 | forall x i, In i (one_bits x) -> ltu i iwordsize = true. |
---|
2569 | Proof. |
---|
2570 | intros. unfold one_bits in H. |
---|
2571 | elim (list_in_map_inv _ _ _ H). intros i0 [EQ IN]. |
---|
2572 | subst i. unfold ltu. unfold iwordsize. apply zlt_true. |
---|
2573 | generalize (Z_one_bits_range _ _ IN). intros. |
---|
2574 | assert (0 <= Z_of_nat wordsize <= max_unsigned). |
---|
2575 | generalize wordsize_pos wordsize_max_unsigned; omega. |
---|
2576 | repeat rewrite unsigned_repr; omega. |
---|
2577 | Qed. |
---|
2578 | |
---|
2579 | Fixpoint int_of_one_bits (l: list int) : int := |
---|
2580 | match l with |
---|
2581 | | nil => zero |
---|
2582 | | a :: b => add (shl one a) (int_of_one_bits b) |
---|
2583 | end. |
---|
2584 | |
---|
2585 | Theorem one_bits_decomp: |
---|
2586 | forall x, x = int_of_one_bits (one_bits x). |
---|
2587 | Proof. |
---|
2588 | intros. |
---|
2589 | transitivity (repr (powerserie (Z_one_bits wordsize (unsigned x) 0))). |
---|
2590 | transitivity (repr (unsigned x)). |
---|
2591 | auto with ints. decEq. apply Z_one_bits_powerserie. |
---|
2592 | auto with ints. |
---|
2593 | unfold one_bits. |
---|
2594 | generalize (Z_one_bits_range (unsigned x)). |
---|
2595 | generalize (Z_one_bits wordsize (unsigned x) 0). |
---|
2596 | induction l. |
---|
2597 | intros; reflexivity. |
---|
2598 | intros; simpl. rewrite <- IHl. unfold add. apply eqm_samerepr. |
---|
2599 | apply eqm_add. rewrite shl_mul_two_p. rewrite mul_commut. |
---|
2600 | rewrite mul_one. apply eqm_unsigned_repr_r. |
---|
2601 | rewrite unsigned_repr. auto with ints. |
---|
2602 | generalize (H a (in_eq _ _)). generalize wordsize_max_unsigned. omega. |
---|
2603 | auto with ints. |
---|
2604 | intros; apply H; auto with coqlib. |
---|
2605 | Qed. |
---|
2606 | |
---|
2607 | (** ** Properties of comparisons *) |
---|
2608 | |
---|
2609 | Theorem negate_cmp: |
---|
2610 | forall c x y, cmp (negate_comparison c) x y = negb (cmp c x y). |
---|
2611 | Proof. |
---|
2612 | intros. destruct c; simpl; try rewrite negb_elim; auto. |
---|
2613 | Qed. |
---|
2614 | |
---|
2615 | Theorem negate_cmpu: |
---|
2616 | forall c x y, cmpu (negate_comparison c) x y = negb (cmpu c x y). |
---|
2617 | Proof. |
---|
2618 | intros. destruct c; simpl; try rewrite negb_elim; auto. |
---|
2619 | Qed. |
---|
2620 | |
---|
2621 | Theorem swap_cmp: |
---|
2622 | forall c x y, cmp (swap_comparison c) x y = cmp c y x. |
---|
2623 | Proof. |
---|
2624 | intros. destruct c; simpl; auto. apply eq_sym. decEq. apply eq_sym. |
---|
2625 | Qed. |
---|
2626 | |
---|
2627 | Theorem swap_cmpu: |
---|
2628 | forall c x y, cmpu (swap_comparison c) x y = cmpu c y x. |
---|
2629 | Proof. |
---|
2630 | intros. destruct c; simpl; auto. apply eq_sym. decEq. apply eq_sym. |
---|
2631 | Qed. |
---|
2632 | |
---|
2633 | Lemma translate_eq: |
---|
2634 | forall x y d, |
---|
2635 | eq (add x d) (add y d) = eq x y. |
---|
2636 | Proof. |
---|
2637 | intros. unfold eq. case (zeq (unsigned x) (unsigned y)); intro. |
---|
2638 | unfold add. rewrite e. apply zeq_true. |
---|
2639 | apply zeq_false. unfold add. red; intro. apply n. |
---|
2640 | apply eqm_small_eq; auto with ints. |
---|
2641 | replace (unsigned x) with ((unsigned x + unsigned d) - unsigned d). |
---|
2642 | replace (unsigned y) with ((unsigned y + unsigned d) - unsigned d). |
---|
2643 | apply eqm_sub. apply eqm_trans with (unsigned (repr (unsigned x + unsigned d))). |
---|
2644 | eauto with ints. apply eqm_trans with (unsigned (repr (unsigned y + unsigned d))). |
---|
2645 | eauto with ints. eauto with ints. eauto with ints. |
---|
2646 | omega. omega. |
---|
2647 | Qed. |
---|
2648 | |
---|
2649 | Lemma translate_lt: |
---|
2650 | forall x y d, |
---|
2651 | min_signed <= signed x + signed d <= max_signed -> |
---|
2652 | min_signed <= signed y + signed d <= max_signed -> |
---|
2653 | lt (add x d) (add y d) = lt x y. |
---|
2654 | Proof. |
---|
2655 | intros. repeat rewrite add_signed. unfold lt. |
---|
2656 | repeat rewrite signed_repr; auto. case (zlt (signed x) (signed y)); intro. |
---|
2657 | apply zlt_true. omega. |
---|
2658 | apply zlt_false. omega. |
---|
2659 | Qed. |
---|
2660 | |
---|
2661 | Theorem translate_cmp: |
---|
2662 | forall c x y d, |
---|
2663 | min_signed <= signed x + signed d <= max_signed -> |
---|
2664 | min_signed <= signed y + signed d <= max_signed -> |
---|
2665 | cmp c (add x d) (add y d) = cmp c x y. |
---|
2666 | Proof. |
---|
2667 | intros. unfold cmp. |
---|
2668 | rewrite translate_eq. repeat rewrite translate_lt; auto. |
---|
2669 | Qed. |
---|
2670 | |
---|
2671 | Theorem notbool_isfalse_istrue: |
---|
2672 | forall x, is_false x -> is_true (notbool x). |
---|
2673 | Proof. |
---|
2674 | unfold is_false, is_true, notbool; intros; subst x. |
---|
2675 | simpl. apply one_not_zero. |
---|
2676 | Qed. |
---|
2677 | |
---|
2678 | Theorem notbool_istrue_isfalse: |
---|
2679 | forall x, is_true x -> is_false (notbool x). |
---|
2680 | Proof. |
---|
2681 | unfold is_false, is_true, notbool; intros. |
---|
2682 | generalize (eq_spec x zero). case (eq x zero); intro. |
---|
2683 | contradiction. auto. |
---|
2684 | Qed. |
---|
2685 | |
---|
2686 | Theorem shru_lt_zero: |
---|
2687 | forall x, |
---|
2688 | shru x (repr (Z_of_nat wordsize - 1)) = if lt x zero then one else zero. |
---|
2689 | Proof. |
---|
2690 | intros. rewrite shru_div_two_p. |
---|
2691 | replace (two_p (unsigned (repr (Z_of_nat wordsize - 1)))) |
---|
2692 | with half_modulus. |
---|
2693 | generalize (unsigned_range x); intro. |
---|
2694 | unfold lt. rewrite signed_zero. unfold signed. |
---|
2695 | destruct (zlt (unsigned x) half_modulus). |
---|
2696 | rewrite zlt_false. |
---|
2697 | replace (unsigned x / half_modulus) with 0. reflexivity. |
---|
2698 | symmetry. apply Zdiv_unique with (unsigned x). ring. omega. omega. |
---|
2699 | rewrite zlt_true. |
---|
2700 | replace (unsigned x / half_modulus) with 1. reflexivity. |
---|
2701 | symmetry. apply Zdiv_unique with (unsigned x - half_modulus). ring. |
---|
2702 | rewrite half_modulus_modulus in H. omega. omega. |
---|
2703 | rewrite unsigned_repr. apply half_modulus_power. |
---|
2704 | generalize wordsize_pos wordsize_max_unsigned; omega. |
---|
2705 | Qed. |
---|
2706 | |
---|
2707 | Theorem ltu_range_test: |
---|
2708 | forall x y, |
---|
2709 | ltu x y = true -> unsigned y <= max_signed -> |
---|
2710 | 0 <= signed x < unsigned y. |
---|
2711 | Proof. |
---|
2712 | intros. |
---|
2713 | unfold ltu in H. destruct (zlt (unsigned x) (unsigned y)); try discriminate. |
---|
2714 | rewrite signed_eq_unsigned. |
---|
2715 | generalize (unsigned_range x). omega. omega. |
---|
2716 | Qed. |
---|
2717 | |
---|
2718 | End Make. |
---|
2719 | |
---|
2720 | (** * Specialization to 32-bit integers. *) |
---|
2721 | |
---|
2722 | Module IntWordsize. |
---|
2723 | Definition wordsize := 32%nat. |
---|
2724 | Remark wordsize_not_zero: wordsize <> 0%nat. |
---|
2725 | Proof. unfold wordsize; congruence. Qed. |
---|
2726 | End IntWordsize. |
---|
2727 | |
---|
2728 | Module Int := Make(IntWordsize). |
---|
2729 | |
---|
2730 | Notation int := Int.int. |
---|
2731 | |
---|
2732 | Remark int_wordsize_divides_modulus: |
---|
2733 | Zdivide (Z_of_nat Int.wordsize) Int.modulus. |
---|
2734 | Proof. |
---|
2735 | exists (two_p (32-5)); reflexivity. |
---|
2736 | Qed. |
---|
2737 | *) |
---|
2738 | |
---|
2739 | |
---|