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Last change
on this file since 415 was
415,
checked in by campbell, 9 years ago
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A couple of amusing examples.
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File size:
1.3 KB
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| Line | |
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| 1 | /* The original Duff's device, with unsupported switch/do combination |
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| 2 | void send(short *to, short *from, int count) |
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| 3 | { |
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| 4 | int n=(count+7)/8; |
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| 5 | switch(count%8){ |
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| 6 | case 0: do{ *to = *from++; |
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| 7 | case 7: *to = *from++; |
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| 8 | case 6: *to = *from++; |
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| 9 | case 5: *to = *from++; |
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| 10 | case 4: *to = *from++; |
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| 11 | case 3: *to = *from++; |
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| 12 | case 2: *to = *from++; |
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| 13 | case 1: *to = *from++; |
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| 14 | }while(--n>0); |
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| 15 | } |
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| 16 | } |
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| 17 | */ |
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| 18 | |
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| 19 | /* The original Duff's device, altered for copying |
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| 20 | void copy(short *to, short *from, int count) |
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| 21 | { |
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| 22 | int n=(count+7)/8; |
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| 23 | switch(count%8){ |
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| 24 | case 0: do{ *to++ = *from++; |
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| 25 | case 7: *to++ = *from++; |
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| 26 | case 6: *to++ = *from++; |
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| 27 | case 5: *to++ = *from++; |
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| 28 | case 4: *to++ = *from++; |
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| 29 | case 3: *to++ = *from++; |
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| 30 | case 2: *to++ = *from++; |
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| 31 | case 1: *to++ = *from++; |
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| 32 | }while(--n>0); |
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| 33 | } |
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| 34 | } |
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| 35 | */ |
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| 36 | |
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| 37 | /* Using goto instead: */ |
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| 38 | void copy(short *to, short *from, int count) |
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| 39 | { |
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| 40 | int n=(count+7)/8; |
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| 41 | switch(count%8){ |
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| 42 | case 0: dolab: *to++ = *from++; |
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| 43 | case 7: *to++ = *from++; |
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| 44 | case 6: *to++ = *from++; |
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| 45 | case 5: *to++ = *from++; |
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| 46 | case 4: *to++ = *from++; |
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| 47 | case 3: *to++ = *from++; |
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| 48 | case 2: *to++ = *from++; |
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| 49 | case 1: *to++ = *from++; |
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| 50 | if (--n>0) goto dolab; |
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| 51 | } |
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| 52 | } |
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| 53 | |
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| 54 | int main(void) { |
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| 55 | short arr1[3] = {1,2,3}; |
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| 56 | short arr2[3]; |
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| 57 | |
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| 58 | copy(arr2,arr1,3); |
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| 59 | |
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| 60 | return arr2[0] + arr2[1] + arr2[2]; |
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| 61 | } |
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