59 lines
1.4 KiB
ArmAsm
59 lines
1.4 KiB
ArmAsm
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/* memcmp() Author: Kees J. Bot */
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/* 2 Jan 1994 */
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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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.text
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.globl _memcmp
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.balign 16
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_memcmp:
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cld
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push %ebp
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movl %esp, %ebp
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push %esi
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push %edi
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movl 8(%ebp), %esi /* String s1 */
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movl 12(%ebp), %edi /* String s2 */
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movl 16(%ebp), %ecx /* Length */
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cmpl $16, %ecx
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jb cbyte /* Don't bother being smart with short arrays */
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movl %esi, %eax
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orl %edi, %eax
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testb $1, %al
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jne cbyte /* Bit 0 set, use byte compare */
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testb $2, %al
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jne cword /* Bit 1 set, use word compare */
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clword:
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shrdl $2, %ecx, %eax /* Save low two bits of ecx in eax */
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shrl $2, %ecx
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repe cmpsl /* Compare longwords */
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subl $4, %esi
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subl $4, %edi
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incl %ecx /* Recompare the last longword */
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shldl $2, %eax, %ecx /* And any excess bytes */
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jmp last
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cword:
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shrdl $1, %ecx, %eax /* Save low bit of ecx in eax */
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shrl $1, %ecx
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repe cmpsw /* Compare words */
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subl $2, %esi
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subl $2, %edi
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incl %ecx /* Recompare the last word */
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shldl $1, %eax, %ecx /* And one more byte? */
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cbyte:
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testl %ecx, %ecx /* Set 'Z' flag if ecx = 0 */
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last:
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repe 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 %ah, %al
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movsbl %al, %eax /* eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1 */
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movl %esi, %edx /* 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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