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| 1 | ! memset() Author: Kees J. Bot
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| 2 | ! 2 Jan 1994
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| 3 | .sect .text; .sect .rom; .sect .data; .sect .bss
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| 4 |
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| 5 | ! void *memset(void *s, int c, size_t n)
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| 6 | ! Set a chunk of memory to the same byte value.
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| 7 | !
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| 8 | .sect .text
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| 9 | .define _memset
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| 10 | .align 16
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| 11 | _memset:
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| 12 | push ebp
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| 13 | mov ebp, esp
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| 14 | push edi
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| 15 | mov edi, 8(ebp) ! The string
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| 16 | movzxb eax, 12(ebp) ! The fill byte
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| 17 | mov ecx, 16(ebp) ! Length
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| 18 | cld
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| 19 | cmp ecx, 16
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| 20 | jb sbyte ! Don't bother being smart with short arrays
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| 21 | test edi, 1
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| 22 | jnz sbyte ! Bit 0 set, use byte store
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| 23 | test edi, 2
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| 24 | jnz sword ! Bit 1 set, use word store
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| 25 | slword: movb ah, al
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| 26 | mov edx, eax
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| 27 | sal edx, 16
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| 28 | or eax, edx ! One byte to four bytes
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| 29 | shrd edx, ecx, 2 ! Save low two bits of ecx in edx
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| 30 | shr ecx, 2
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| 31 | rep
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| 32 | stos ! Store longwords.
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| 33 | shld ecx, edx, 2 ! Restore low two bits
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| 34 | sword: movb ah, al ! One byte to two bytes
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| 35 | shr ecx, 1
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| 36 | rep
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| 37 | o16 stos ! Store words
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| 38 | adc ecx, ecx ! One more byte?
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| 39 | sbyte: rep
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| 40 | stosb ! Store bytes
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| 41 | done: mov eax, 8(ebp) ! Return some value you have no need for
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| 42 | pop edi
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| 43 | pop ebp
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| 44 | ret
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