bcmp.c revision 116189 
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: head/sys/libkern/bcmp.c 116189 2003-06-11 05:37:42Z obrien $");
36
37#include <sys/libkern.h>
38#include <machine/endian.h>
39
40typedef	const void	*cvp;
41typedef	const unsigned char	*ustring;
42typedef unsigned long	ul;
43typedef const unsigned long	*culp;
44
45/*
46 * bcmp -- vax cmpc3 instruction
47 */
48int
49bcmp(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}
151