56 lines
1.3 KiB
ArmAsm
56 lines
1.3 KiB
ArmAsm
! memcmp() 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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! int memcmp(const void *s1, const void *s2, size_t n)
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! Compare two chunks of memory.
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!
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.sect .text
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.define _memcmp
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.align 16
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_memcmp:
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cld
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push ebp
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mov ebp, esp
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push esi
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push edi
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mov esi, 8(ebp) ! String s1
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mov edi, 12(ebp) ! String s2
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mov ecx, 16(ebp) ! Length
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cmp ecx, 16
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jb cbyte ! Don't bother being smart with short arrays
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mov eax, esi
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or eax, edi
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testb al, 1
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jnz cbyte ! Bit 0 set, use byte compare
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testb al, 2
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jnz cword ! Bit 1 set, use word compare
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clword: shrd eax, ecx, 2 ! Save low two bits of ecx in eax
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shr ecx, 2
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repe
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cmps ! Compare longwords
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sub esi, 4
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sub edi, 4
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inc ecx ! Recompare the last longword
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shld ecx, eax, 2 ! And any excess bytes
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jmp last
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cword: shrd eax, ecx, 1 ! Save low bit of ecx in eax
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shr ecx, 1
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repe
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o16 cmps ! Compare words
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sub esi, 2
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sub edi, 2
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inc ecx ! Recompare the last word
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shld ecx, eax, 1 ! And one more byte?
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cbyte: test ecx, ecx ! Set 'Z' flag if ecx = 0
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last: repe
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cmpsb ! Look for the first differing byte
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seta al ! al = (s1 > s2)
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setb ah ! ah = (s1 < s2)
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subb al, ah
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movsxb eax, al ! eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1
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mov edx, esi ! For bcmp() to play with
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pop edi
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pop esi
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pop ebp
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ret
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