1 // SPDX-License-Identifier: BSD-3-Clause
2 /*
3  * Copyright (c) 1994-2009  Red Hat, Inc.
4  * All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions are met:
8  *
9  * 1. Redistributions of source code must retain the above copyright notice,
10  * this list of conditions and the following disclaimer.
11  *
12  * 2. Redistributions in binary form must reproduce the above copyright notice,
13  * this list of conditions and the following disclaimer in the documentation
14  * and/or other materials provided with the distribution.
15  *
16  * 3. Neither the name of the copyright holder nor the names of its
17  * contributors may be used to endorse or promote products derived from this
18  * software without specific prior written permission.
19  *
20  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
21  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
24  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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28  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
30  * POSSIBILITY OF SUCH DAMAGE.
31  */
32 
33 /*
34 FUNCTION
35 	<<memcmp>>---compare two memory areas
36 
37 INDEX
38 	memcmp
39 
40 ANSI_SYNOPSIS
41 	#include <string.h>
42 	int memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>);
43 
44 TRAD_SYNOPSIS
45 	#include <string.h>
46 	int memcmp(<[s1]>, <[s2]>, <[n]>)
47 	void *<[s1]>;
48 	void *<[s2]>;
49 	size_t <[n]>;
50 
51 DESCRIPTION
52 	This function compares not more than <[n]> characters of the
53 	object pointed to by <[s1]> with the object pointed to by <[s2]>.
54 
55 RETURNS
56 	The function returns an integer greater than, equal to or
57 	less than zero 	according to whether the object pointed to by
58 	<[s1]> is greater than, equal to or less than the object
59 	pointed to by <[s2]>.
60 
61 PORTABILITY
62 <<memcmp>> is ANSI C.
63 
64 <<memcmp>> requires no supporting OS subroutines.
65 
66 QUICKREF
67 	memcmp ansi pure
68 */
69 
70 #include "_ansi.h"
71 #include <string.h>
72 
73 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
74 #define UNALIGNED(X, Y) \
75 	(((long)X & (sizeof(long) - 1)) | ((long)Y & (sizeof(long) - 1)))
76 
77 /* How many bytes are copied each iteration of the word copy loop.  */
78 #define LBLOCKSIZE (sizeof(long))
79 
80 /* Threshhold for punting to the byte copier.  */
81 #define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
82 
83 int
84 _DEFUN(memcmp, (m1, m2, n), _CONST _PTR m1 _AND _CONST _PTR m2 _AND size_t n)
85 {
86 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
87 	unsigned char *s1 = (unsigned char *)m1;
88 	unsigned char *s2 = (unsigned char *)m2;
89 
90 	while (n--) {
91 		if (*s1 != *s2)
92 			return *s1 - *s2;
93 		s1++;
94 		s2++;
95 	}
96 	return 0;
97 #else
98 	unsigned char *s1 = (unsigned char *)m1;
99 	unsigned char *s2 = (unsigned char *)m2;
100 	unsigned long *a1;
101 	unsigned long *a2;
102 
103 	/* If the size is too small, or either pointer is unaligned,
104 	   then we punt to the byte compare loop.  Hopefully this will
105 	   not turn up in inner loops.  */
106 	if (!TOO_SMALL(n) && !UNALIGNED(s1, s2)) {
107 		/*
108 		 * Otherwise, load and compare the blocks of memory one word at
109 		 * a time.
110 		 */
111 		a1 = (unsigned long *)s1;
112 		a2 = (unsigned long *)s2;
113 		while (n >= LBLOCKSIZE) {
114 			if (*a1 != *a2)
115 				break;
116 			a1++;
117 			a2++;
118 			n -= LBLOCKSIZE;
119 		}
120 
121 		/* check m mod LBLOCKSIZE remaining characters */
122 
123 		s1 = (unsigned char *)a1;
124 		s2 = (unsigned char *)a2;
125 	}
126 
127 	while (n--) {
128 		if (*s1 != *s2)
129 			return *s1 - *s2;
130 		s1++;
131 		s2++;
132 	}
133 
134 	return 0;
135 #endif /* not PREFER_SIZE_OVER_SPEED */
136 }
137