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("$FreeBSD$");
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
57void *
58memcchr(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
106done:
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}
116