45 lines
1015 B
ArmAsm
45 lines
1015 B
ArmAsm
! memset() Author: Kees J. Bot
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! 2 Jan 1994
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.sect .text; .sect .rom; .sect .data; .sect .bss
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! void *memset(void *s, int c, size_t n)
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! Set a chunk of memory to the same byte value.
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!
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.sect .text
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.define _memset
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.align 16
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_memset:
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push ebp
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mov ebp, esp
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push edi
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mov edi, 8(ebp) ! The string
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movzxb eax, 12(ebp) ! The fill byte
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mov ecx, 16(ebp) ! Length
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cld
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cmp ecx, 16
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jb sbyte ! Don't bother being smart with short arrays
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test edi, 1
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jnz sbyte ! Bit 0 set, use byte store
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test edi, 2
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jnz sword ! Bit 1 set, use word store
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slword: movb ah, al
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mov edx, eax
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sal edx, 16
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or eax, edx ! One byte to four bytes
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shrd edx, ecx, 2 ! Save low two bits of ecx in edx
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shr ecx, 2
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rep
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stos ! Store longwords.
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shld ecx, edx, 2 ! Restore low two bits
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sword: movb ah, al ! One byte to two bytes
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shr ecx, 1
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rep
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o16 stos ! Store words
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adc ecx, ecx ! One more byte?
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sbyte: rep
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stosb ! Store bytes
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done: mov eax, 8(ebp) ! Return some value you have no need for
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pop edi
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pop ebp
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ret
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