bcmp.c revision 319286 
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: stable/10/sys/libkern/bcmp.c 319286 2017-05-31 06:00:14Z delphij $");
32
33#include <sys/libkern.h>
34#include <machine/endian.h>
35
36typedef	const void	*cvp;
37typedef	const unsigned char	*ustring;
38typedef unsigned long	ul;
39typedef const unsigned long	*culp;
40
41/*
42 * bcmp -- vax cmpc3 instruction
43 */
44int
45bcmp(b1, b2, length)
46	const void *b1, *b2;
47	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