48 lines
1.4 KiB
ArmAsm
48 lines
1.4 KiB
ArmAsm
# memset() Author: Kees J. Bot
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# 2 Jan 1994
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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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.intel_syntax
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.global _memset
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.text
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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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movzx eax, byte ptr [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:
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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 stosd # Store longwords.
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shld ecx, edx, 2 # Restore low two bits
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sword:
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movb ah, al # One byte to two bytes
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shr ecx, 1
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rep stosw # Store words
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adc ecx, ecx # One more byte?
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sbyte:
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rep stosb # Store bytes
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done:
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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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