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/* Compare two memory blocks for differences in the first COUNT bytes.
Copyright (C) 1995-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include "asm-syntax.h"
#define PARMS 4+4 /* space for 1 saved reg */
#define BLK1 PARMS
#define BLK2 BLK1+4
#define LEN BLK2+4
.text
ENTRY (memcmp)
pushl %esi /* Save callee-safe registers. */
cfi_adjust_cfa_offset (4)
movl %edi, %edx /* Note that %edx is not used and can
so be used to save %edi. It's faster. */
cfi_register (edi, edx)
movl BLK1(%esp), %esi
cfi_rel_offset (esi, 0)
movl BLK2(%esp), %edi
movl LEN(%esp), %ecx
cld /* Set direction of comparison. */
xorl %eax, %eax /* Default result. */
repe /* Compare at most %ecx bytes. */
cmpsb
jz L(1) /* If even last byte was equal we return 0. */
/* The memory blocks are not equal. So result of the last
subtraction is present in the carry flag. It is set when
the byte in block #2 is bigger. In this case we have to
return -1 (=0xffffffff), else 1. */
sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set
or not depending on last subtraction. */
/* At this point %eax == 0, if the byte of block #1 was bigger, and
0xffffffff if the last byte of block #2 was bigger. The latter
case is already correct but the former needs a little adjustment.
Note that the following operation does not change 0xffffffff. */
orb $1, %al /* Change 0 to 1. */
L(1): popl %esi /* Restore registers. */
cfi_adjust_cfa_offset (-4)
cfi_restore (esi)
movl %edx, %edi
cfi_restore (edi)
ret
END (memcmp)
#undef bcmp
weak_alias (memcmp, bcmp)
#undef __memcmpeq
strong_alias (memcmp, __memcmpeq)
libc_hidden_builtin_def (memcmp)
libc_hidden_def (__memcmpeq)
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