FreeBSD/Linux Kernel Cross Reference
sys/libkern/memcchr.c
1 /*-
2 * Copyright (c) 2012 Ed Schouten <ed@FreeBSD.org>
3 * 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 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD: releng/11.2/sys/libkern/memcchr.c 229198 2012-01-01 20:26:11Z ed $");
29
30 #include <sys/libkern.h>
31 #include <sys/limits.h>
32 #include <sys/param.h>
33
34 /*
35 * memcchr(): find first character in buffer not matching `c'.
36 *
37 * This function performs the complement of memchr(). To provide decent
38 * performance, this function compares data from the buffer one word at
39 * a time.
40 *
41 * This code is inspired by libc's strlen(), written by Xin Li.
42 */
43
44 #if LONG_BIT != 32 && LONG_BIT != 64
45 #error Unsupported word size
46 #endif
47
48 #define LONGPTR_MASK (sizeof(long) - 1)
49
50 #define TESTBYTE \
51 do { \
52 if (*p != (unsigned char)c) \
53 goto done; \
54 p++; \
55 } while (0)
56
57 void *
58 memcchr(const void *begin, int c, size_t n)
59 {
60 const unsigned long *lp;
61 const unsigned char *p, *end;
62 unsigned long word;
63
64 /* Four or eight repetitions of `c'. */
65 word = (unsigned char)c;
66 word |= word << 8;
67 word |= word << 16;
68 #if LONG_BIT >= 64
69 word |= word << 32;
70 #endif
71
72 /* Don't perform memory I/O when passing a zero-length buffer. */
73 if (n == 0)
74 return (NULL);
75
76 /*
77 * First determine whether there is a character unequal to `c'
78 * in the first word. As this word may contain bytes before
79 * `begin', we may execute this loop spuriously.
80 */
81 lp = (const unsigned long *)((uintptr_t)begin & ~LONGPTR_MASK);
82 end = (const unsigned char *)begin + n;
83 if (*lp++ != word)
84 for (p = begin; p < (const unsigned char *)lp;)
85 TESTBYTE;
86
87 /* Now compare the data one word at a time. */
88 for (; (const unsigned char *)lp < end; lp++) {
89 if (*lp != word) {
90 p = (const unsigned char *)lp;
91 TESTBYTE;
92 TESTBYTE;
93 TESTBYTE;
94 #if LONG_BIT >= 64
95 TESTBYTE;
96 TESTBYTE;
97 TESTBYTE;
98 TESTBYTE;
99 #endif
100 goto done;
101 }
102 }
103
104 return (NULL);
105
106 done:
107 /*
108 * If the end of the buffer is not word aligned, the previous
109 * loops may obtain an address that's beyond the end of the
110 * buffer.
111 */
112 if (p < end)
113 return (__DECONST(void *, p));
114 return (NULL);
115 }
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