1 /* Compare two memory blocks for differences in the first COUNT bytes.
2 Copyright (C) 1995,1996,1997,2000,2004,2005 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 Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the 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 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
20 #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
30 ENTRY (BP_SYM (memcmp))
33 pushl %esi /* Save callee-safe registers. */
34 cfi_adjust_cfa_offset (4)
35 movl %edi, %edx /* Note that %edx is not used and can
36 so be used to save %edi. It's faster. */
37 cfi_register (edi, edx)
40 cfi_rel_offset (esi, 0)
43 CHECK_BOUNDS_LOW (%esi, BLK1(%esp))
44 CHECK_BOUNDS_LOW (%edi, BLK2(%esp))
46 cld /* Set direction of comparison. */
48 xorl %eax, %eax /* Default result. */
50 repe /* Compare at most %ecx bytes. */
52 jz L(1) /* If even last byte was equal we return 0. */
54 /* The memory blocks are not equal. So result of the last
55 subtraction is present in the carry flag. It is set when
56 the byte in block #2 is bigger. In this case we have to
57 return -1 (=0xffffffff), else 1. */
58 sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set
59 or not depending on last subtraction. */
61 /* At this point %eax == 0, if the byte of block #1 was bigger, and
62 0xffffffff if the last byte of block #2 was bigger. The latter
63 case is already correct but the former needs a little adjustment.
64 Note that the following operation does not change 0xffffffff. */
65 orb $1, %al /* Change 0 to 1. */
67 L(1): CHECK_BOUNDS_HIGH (%esi, BLK1(%esp), jbe)
68 CHECK_BOUNDS_HIGH (%edi, BLK2(%esp), jbe)
69 popl %esi /* Restore registers. */
70 cfi_adjust_cfa_offset (-4)
80 weak_alias (BP_SYM (memcmp), BP_SYM (bcmp))
81 libc_hidden_builtin_def (BP_SYM (memcmp))