FreeBSD/Linux Kernel Cross Reference
sys/libkern/bcmp.c
1 /*
2 * Copyright (c) 1987, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD: releng/5.2/sys/libkern/bcmp.c 116189 2003-06-11 05:37:42Z obrien $");
36
37 #include <sys/libkern.h>
38 #include <machine/endian.h>
39
40 typedef const void *cvp;
41 typedef const unsigned char *ustring;
42 typedef unsigned long ul;
43 typedef const unsigned long *culp;
44
45 /*
46 * bcmp -- vax cmpc3 instruction
47 */
48 int
49 bcmp(b1, b2, length)
50 const void *b1, *b2;
51 register size_t length;
52 {
53 #if BYTE_ORDER == LITTLE_ENDIAN
54 /*
55 * The following code is endian specific. Changing it from
56 * little-endian to big-endian is fairly trivial, but making
57 * it do both is more difficult.
58 *
59 * Note that this code will reference the entire longword which
60 * includes the final byte to compare. I don't believe this is
61 * a problem since AFAIK, objects are not protected at smaller
62 * than longword boundaries.
63 */
64 int shl, shr, len = length;
65 ustring p1 = b1, p2 = b2;
66 ul va, vb;
67
68 if (len == 0)
69 return (0);
70
71 /*
72 * align p1 to a longword boundary
73 */
74 while ((long)p1 & (sizeof(long) - 1)) {
75 if (*p1++ != *p2++)
76 return (1);
77 if (--len <= 0)
78 return (0);
79 }
80
81 /*
82 * align p2 to longword boundary and calculate the shift required to
83 * align p1 and p2
84 */
85 shr = (long)p2 & (sizeof(long) - 1);
86 if (shr != 0) {
87 p2 -= shr; /* p2 now longword aligned */
88 shr <<= 3; /* offset in bits */
89 shl = (sizeof(long) << 3) - shr;
90
91 va = *(culp)p2;
92 p2 += sizeof(long);
93
94 while ((len -= sizeof(long)) >= 0) {
95 vb = *(culp)p2;
96 p2 += sizeof(long);
97 if (*(culp)p1 != (va >> shr | vb << shl))
98 return (1);
99 p1 += sizeof(long);
100 va = vb;
101 }
102 /*
103 * At this point, len is between -sizeof(long) and -1,
104 * representing 0 .. sizeof(long)-1 bytes remaining.
105 */
106 if (!(len += sizeof(long)))
107 return (0);
108
109 len <<= 3; /* remaining length in bits */
110 /*
111 * The following is similar to the `if' condition
112 * inside the above while loop. The ?: is necessary
113 * to avoid accessing the longword after the longword
114 * containing the last byte to be compared.
115 */
116 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
117 *(culp)p1) & ((1L << len) - 1)) != 0);
118 } else {
119 /* p1 and p2 have common alignment so no shifting needed */
120 while ((len -= sizeof(long)) >= 0) {
121 if (*(culp)p1 != *(culp)p2)
122 return (1);
123 p1 += sizeof(long);
124 p2 += sizeof(long);
125 }
126
127 /*
128 * At this point, len is between -sizeof(long) and -1,
129 * representing 0 .. sizeof(long)-1 bytes remaining.
130 */
131 if (!(len += sizeof(long)))
132 return (0);
133
134 return (((*(culp)p1 ^ *(culp)p2)
135 & ((1L << (len << 3)) - 1)) != 0);
136 }
137 #else
138 register char *p1, *p2;
139
140 if (length == 0)
141 return(0);
142 p1 = (char *)b1;
143 p2 = (char *)b2;
144 do
145 if (*p1++ != *p2++)
146 break;
147 while (--length);
148 return(length);
149 #endif
150 }
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