| 1,59 → 1,57 |
|---|
| # memcmp() Author: Kees J. Bot |
| # 2 Jan 1994 |
| /* memcmp() Author: Kees J. Bot */ |
| /* 2 Jan 1994 */ |
| |
| # int memcmp(const void *s1, const void *s2, size_t n) |
| # Compare two chunks of memory. |
| # |
| /* int memcmp(const void *s1, const void *s2, size_t n) */ |
| /* Compare two chunks of memory. */ |
| /* */ |
| #include "asm.h" |
| |
| .intel_syntax |
| ENTRY(memcmp) |
| cld |
| push %ebp |
| movl %esp, %ebp |
| push %esi |
| push %edi |
| movl 8(%ebp), %esi /* String s1 */ |
| movl 12(%ebp), %edi /* String s2 */ |
| movl 16(%ebp), %ecx /* Length */ |
| cmpl $16, %ecx |
| jb cbyte /* Don't bother being smart with short arrays */ |
| movl %esi, %eax |
| orl %edi, %eax |
| testb $1, %al |
| jne cbyte /* Bit 0 set, use byte compare */ |
| testb $2, %al |
| jne cword /* Bit 1 set, use word compare */ |
| clword: |
| shrdl $2, %ecx, %eax /* Save low two bits of ecx in eax */ |
| shrl $2, %ecx |
| |
| .globl _memcmp |
| repe cmpsl /* Compare longwords */ |
| subl $4, %esi |
| subl $4, %edi |
| incl %ecx /* Recompare the last longword */ |
| shldl $2, %eax, %ecx /* And any excess bytes */ |
| jmp last |
| cword: |
| shrdl $1, %ecx, %eax /* Save low bit of ecx in eax */ |
| shrl $1, %ecx |
| |
| .text |
| .align 16 |
| _memcmp: |
| cld |
| push ebp |
| mov ebp, esp |
| push esi |
| push edi |
| mov esi, [8+ebp] # String s1 |
| mov edi, [12+ebp] # String s2 |
| mov ecx, [16+ebp] # Length |
| cmp ecx, 16 |
| jb cbyte # Don't bother being smart with short arrays |
| mov eax, esi |
| or eax, edi |
| testb al, 1 |
| jnz cbyte # Bit 0 set, use byte compare |
| testb al, 2 |
| jnz cword # Bit 1 set, use word compare |
| clword: shrd eax, ecx, 2 # Save low two bits of ecx in eax |
| shr ecx, 2 |
| repe |
| cmpsd # Compare longwords |
| sub esi, 4 |
| sub edi, 4 |
| inc ecx # Recompare the last longword |
| shld ecx, eax, 2 # And any excess bytes |
| jmp last |
| cword: shrd eax, ecx, 1 # Save low bit of ecx in eax |
| shr ecx, 1 |
| repe |
| cmpsw # Compare words |
| sub esi, 2 |
| sub edi, 2 |
| inc ecx # Recompare the last word |
| shld ecx, eax, 1 # And one more byte? |
| cbyte: test ecx, ecx # Set 'Z' flag if ecx = 0 |
| last: repe |
| cmpsb # Look for the first differing byte |
| seta al # al = (s1 > s2) |
| setb ah # ah = (s1 < s2) |
| subb al, ah |
| movsxb eax, al # eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1 |
| mov edx, esi # For bcmp() to play with |
| pop edi |
| pop esi |
| pop ebp |
| repe cmpsw /* Compare words */ |
| subl $2, %esi |
| subl $2, %edi |
| incl %ecx /* Recompare the last word */ |
| shldl $1, %eax, %ecx /* And one more byte? */ |
| cbyte: |
| testl %ecx, %ecx /* Set 'Z' flag if ecx = 0 */ |
| last: |
| repe cmpsb /* Look for the first differing byte */ |
| seta %al /* al = (s1 > s2) */ |
| setb %ah /* ah = (s1 < s2) */ |
| subb %ah, %al |
| movsbl %al, %eax /* eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1 */ |
| movl %esi, %edx /* For bcmp() to play with */ |
| pop %edi |
| pop %esi |
| pop %ebp |
| ret |