1 /* Compare two memory blocks for differences in the first COUNT bytes.
2 Copyright (C) 1995, 1996, 1997, 2000 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Library General Public License as
7 published by the Free Software Foundation; either version 2 of the
8 License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Library General Public License for more details.
15 You should have received a copy of the GNU Library General Public
16 License along with the GNU C Library; see the file COPYING.LIB. If not,
17 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 Boston, MA 02111-1307, USA. */
21 #include "asm-syntax.h"
24 #define PARMS LINKAGE+4 /* space for 1 saved reg */
26 #define BLK2 BLK1+PTR_SIZE
27 #define LEN BLK2+PTR_SIZE
33 pushl %esi /* Save callee-safe registers. */
34 movl %edi, %edx /* Note that %edx is not used and can
35 so be used to save %edi. It's faster. */
41 cld /* Set direction of comparison. */
43 xorl %eax, %eax /* Default result. */
45 repe /* Compare at most %ecx bytes. */
47 jz L(1) /* If even last byte was equal we return 0. */
49 /* The memory blocks are not equal. So result of the last
50 subtraction is present in the carry flag. It is set when
51 the byte in block #2 is bigger. In this case we have to
52 return -1 (=0xffffffff), else 1. */
53 sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set
54 or not depending on last subtraction. */
56 /* At this point %eax == 0, if the byte of block #1 was bigger, and
57 0xffffffff if the last byte of block #2 was bigger. The latter
58 case is already correct but the former needs a little adjustment.
59 Note that the following operation does not change 0xffffffff. */
60 orb $1, %al /* Change 0 to 1. */
62 L(1): popl %esi /* Restore registers. */
70 weak_alias (memcmp, bcmp)