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69 lines
2.3 KiB
ArmAsm
69 lines
2.3 KiB
ArmAsm
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/* memcmp -- compare two memory blocks for differences in the first COUNT
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bytes.
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Copyright (C) 1995 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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <sysdep.h>
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#include "asm-syntax.h"
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/*
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INPUT PARAMETERS:
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block1 (sp + 4)
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block2 (sp + 8)
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len (sp + 12)
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*/
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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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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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movl 12(%esp), %esi /* Load address of block #1. */
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movl 16(%esp), %edi /* Load address of block #2. */
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movl 20(%esp), %ecx /* Load maximal length of compare area. */
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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 L1 /* 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 later
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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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L1: popl %esi /* Restore registers. */
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movl %edx, %edi
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ret
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#undef bcmp
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weak_alias (memcmp, bcmp)
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