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 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 #include <sys/cdefs.h>
31 __FBSDID("$FreeBSD: src/sys/libkern/bcmp.c,v 1.11 2005/01/07 00:24:32 imp Exp $");
32
33 #include <sys/libkern.h>
34 #include <machine/endian.h>
35
36 typedef const void *cvp;
37 typedef const unsigned char *ustring;
38 typedef unsigned long ul;
39 typedef const unsigned long *culp;
40
41 /*
42 * bcmp -- vax cmpc3 instruction
43 */
44 int
45 bcmp(b1, b2, length)
46 const void *b1, *b2;
47 register size_t length;
48 {
49 #if BYTE_ORDER == LITTLE_ENDIAN
50 /*
51 * The following code is endian specific. Changing it from
52 * little-endian to big-endian is fairly trivial, but making
53 * it do both is more difficult.
54 *
55 * Note that this code will reference the entire longword which
56 * includes the final byte to compare. I don't believe this is
57 * a problem since AFAIK, objects are not protected at smaller
58 * than longword boundaries.
59 */
60 int shl, shr, len = length;
61 ustring p1 = b1, p2 = b2;
62 ul va, vb;
63
64 if (len == 0)
65 return (0);
66
67 /*
68 * align p1 to a longword boundary
69 */
70 while ((long)p1 & (sizeof(long) - 1)) {
71 if (*p1++ != *p2++)
72 return (1);
73 if (--len <= 0)
74 return (0);
75 }
76
77 /*
78 * align p2 to longword boundary and calculate the shift required to
79 * align p1 and p2
80 */
81 shr = (long)p2 & (sizeof(long) - 1);
82 if (shr != 0) {
83 p2 -= shr; /* p2 now longword aligned */
84 shr <<= 3; /* offset in bits */
85 shl = (sizeof(long) << 3) - shr;
86
87 va = *(culp)p2;
88 p2 += sizeof(long);
89
90 while ((len -= sizeof(long)) >= 0) {
91 vb = *(culp)p2;
92 p2 += sizeof(long);
93 if (*(culp)p1 != (va >> shr | vb << shl))
94 return (1);
95 p1 += sizeof(long);
96 va = vb;
97 }
98 /*
99 * At this point, len is between -sizeof(long) and -1,
100 * representing 0 .. sizeof(long)-1 bytes remaining.
101 */
102 if (!(len += sizeof(long)))
103 return (0);
104
105 len <<= 3; /* remaining length in bits */
106 /*
107 * The following is similar to the `if' condition
108 * inside the above while loop. The ?: is necessary
109 * to avoid accessing the longword after the longword
110 * containing the last byte to be compared.
111 */
112 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
113 *(culp)p1) & ((1L << len) - 1)) != 0);
114 } else {
115 /* p1 and p2 have common alignment so no shifting needed */
116 while ((len -= sizeof(long)) >= 0) {
117 if (*(culp)p1 != *(culp)p2)
118 return (1);
119 p1 += sizeof(long);
120 p2 += sizeof(long);
121 }
122
123 /*
124 * At this point, len is between -sizeof(long) and -1,
125 * representing 0 .. sizeof(long)-1 bytes remaining.
126 */
127 if (!(len += sizeof(long)))
128 return (0);
129
130 return (((*(culp)p1 ^ *(culp)p2)
131 & ((1L << (len << 3)) - 1)) != 0);
132 }
133 #else
134 const char *p1, *p2;
135
136 if (length == 0)
137 return(0);
138 p1 = b1;
139 p2 = b2;
140 do
141 if (*p1++ != *p2++)
142 break;
143 while (--length);
144 return(length);
145 #endif
146 }
147
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