source: Deliverables/D4.1/physical.ml @ 107

exception Byte7_conversion

module Byte7Map =
  Map.Make (struct type t = byte7 let compare = Pervasives.compare end)
module WordMap =
  Map.Make (struct type t = word let compare = Pervasives.compare end)

let int_of_bit =
  function
    false -> 0
  | true -> 1

let byte7_of_byte b =
  let n1,n2 = from_byte b in
    match from_nibble n1 with
      (false,b1,b2,b3) -> mk_byte7 b1 b2 b3 n2
    | _ -> raise Byte7_conversion

let add8_with_c (b1 : [`Eight] vect) (b2 : [`Eight] vect) (c : bit) =
 let n1 = int_of_vect b1 in
 let n2 = int_of_vect b2 in
 let c = int_of_bit c in
 let res = n1 + n2 + c in
 let ac = n1 mod 16 + n2 mod 16 + c >= 16 in
 let c6 = n1 mod 128 + n2 mod 128 + c >= 128 in
 let res,c = res mod 256, res >= 256 in
 let ov = c <> c6 in
   vect_of_int res `Eight,c,ac,ov
;;

let subb8_with_c (b1 : [`Eight] vect) (b2 : [`Eight] vect) (c : bit) =
 let n1 = int_of_vect b1 in
 let n2 = int_of_vect b2 in
 let c = int_of_bit c in
 let res = n1 - n2 - c in
 let ac = n1 mod 16 - n2 mod 16 - c < 0 in
 let c6 = n1 mod 128 - n2 mod 128 - c < 0 in
 let res,c =
  if res >= 0 then res,false
  else n1 + 256 - n2 - c, true in
 let ov = c <> c6 in
  (vect_of_int res `Eight,c,ac,ov)
;;

let dec b =
 let res = int_of_vect b - 1 in
  if res < 0 then vect_of_int 255 `Eight
  else vect_of_int res `Eight
;;

let inc b =
 let res = int_of_vect b + 1 in
  if res > 255 then (vect_of_int 0 `Eight : byte)
  else (vect_of_int res `Eight : byte)
;;

let byte7_of_bit b =
  [false;false;false;false;false;false;b]
;;

let byte_of_byte7 =
 function
    ([b1;b2;b3]::n) -> [false;b1;b2;b3]::n
  | _ -> assert false
;;