1/* Compare two memory blocks for differences in the first COUNT bytes.
2   Copyright (C) 1995-2021 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
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.
9
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.
14
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   <https://www.gnu.org/licenses/>.  */
18
19#include <sysdep.h>
20#include "asm-syntax.h"
21
22#define PARMS	4+4	/* space for 1 saved reg */
23#define BLK1	PARMS
24#define BLK2	BLK1+4
25#define LEN	BLK2+4
26
27	.text
28ENTRY (memcmp)
29
30	pushl %esi		/* Save callee-safe registers.  */
31	cfi_adjust_cfa_offset (4)
32	movl %edi, %edx		/* Note that %edx is not used and can
33				   so be used to save %edi.  It's faster.  */
34	cfi_register (edi, edx)
35
36	movl BLK1(%esp), %esi
37	cfi_rel_offset (esi, 0)
38	movl BLK2(%esp), %edi
39	movl LEN(%esp), %ecx
40
41	cld			/* Set direction of comparison.  */
42
43	xorl %eax, %eax		/* Default result.  */
44
45	repe			/* Compare at most %ecx bytes.  */
46	cmpsb
47	jz L(1)			/* If even last byte was equal we return 0.  */
48
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.  */
55
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.  */
61
62L(1):	popl %esi		/* Restore registers.  */
63	cfi_adjust_cfa_offset (-4)
64	cfi_restore (esi)
65	movl %edx, %edi
66	cfi_restore (edi)
67
68	ret
69END (memcmp)
70
71#undef bcmp
72weak_alias (memcmp, bcmp)
73#undef __memcmpeq
74strong_alias (memcmp, __memcmpeq)
75libc_hidden_builtin_def (memcmp)
76libc_hidden_def (__memcmpeq)
77