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77 lines
2.4 KiB
ArmAsm
77 lines
2.4 KiB
ArmAsm
/* Compare two memory blocks for differences in the first COUNT bytes.
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Copyright (C) 1995-2023 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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#include "asm-syntax.h"
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#define PARMS 4+4 /* space for 1 saved reg */
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#define BLK1 PARMS
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#define BLK2 BLK1+4
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#define LEN BLK2+4
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.text
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ENTRY (memcmp)
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pushl %esi /* Save callee-safe registers. */
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cfi_adjust_cfa_offset (4)
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movl %edi, %edx /* Note that %edx is not used and can
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so be used to save %edi. It's faster. */
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cfi_register (edi, edx)
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movl BLK1(%esp), %esi
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cfi_rel_offset (esi, 0)
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movl BLK2(%esp), %edi
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movl LEN(%esp), %ecx
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cld /* Set direction of comparison. */
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xorl %eax, %eax /* Default result. */
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repe /* Compare at most %ecx bytes. */
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cmpsb
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jz L(1) /* If even last byte was equal we return 0. */
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/* The memory blocks are not equal. So result of the last
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subtraction is present in the carry flag. It is set when
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the byte in block #2 is bigger. In this case we have to
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return -1 (=0xffffffff), else 1. */
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sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set
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or not depending on last subtraction. */
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/* At this point %eax == 0, if the byte of block #1 was bigger, and
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0xffffffff if the last byte of block #2 was bigger. The latter
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case is already correct but the former needs a little adjustment.
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Note that the following operation does not change 0xffffffff. */
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orb $1, %al /* Change 0 to 1. */
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L(1): popl %esi /* Restore registers. */
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cfi_adjust_cfa_offset (-4)
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cfi_restore (esi)
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movl %edx, %edi
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cfi_restore (edi)
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ret
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END (memcmp)
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#undef bcmp
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weak_alias (memcmp, bcmp)
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#undef __memcmpeq
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strong_alias (memcmp, __memcmpeq)
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libc_hidden_builtin_def (memcmp)
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libc_hidden_def (__memcmpeq)
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