45 lines
981 B
ArmAsm
Executable file
45 lines
981 B
ArmAsm
Executable file
! memcmp() Author: Kees J. Bot
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! 27 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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_memcmp:
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cld
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push bp
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mov bp, sp
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push si
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push di
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xor ax, ax ! Prepare return value
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mov si, 4(bp) ! String s1
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mov di, 6(bp) ! String s2
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mov cx, 8(bp) ! Length
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cmp cx, #16
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jb cbyte ! Don't bother being smart with short arrays
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mov dx, si
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or dx, di
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andb dl, #1
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jnz cbyte ! Bit 0 set, use byte compare
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cword: sar cx, #1
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adcb dl, dl ! Save carry
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repe cmps ! Compare words
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mov cx, #2 ! Recompare the last word
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sub si, cx
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sub di, cx
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addb cl, dl ! One more byte?
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cbyte: test cx, cx ! Set 'Z' flag if cx = 0
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last:
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repe cmpsb ! Look for the first differing byte
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je equal
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ja after
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sub ax, #2 ! if (s1 < s2) ax -= 2;
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after: inc ax ! ax++, now it's -1 or 1
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equal: mov dx, si ! For bcmp() to play with
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pop di
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pop si
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pop bp
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ret
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