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 * $FreeBSD: src/sys/libkern/memcchr.c,v 1.1 2012/01/01 20:26:11 ed Exp $ 27 * 28 */ 29 30 #include <sys/cdefs.h> 31 32 #include <sys/libkern.h> 33 #include <sys/limits.h> 34 #include <sys/param.h> 35 36 /* 37 * memcchr(): find first character in buffer not matching `c'. 38 * 39 * This function performs the complement of memchr(). To provide decent 40 * performance, this function compares data from the buffer one word at 41 * a time. 42 * 43 * This code is inspired by libc's strlen(), written by Xin Li. 44 */ 45 46 #if LONG_BIT != 32 && LONG_BIT != 64 47 #error Unsupported word size 48 #endif 49 50 #define LONGPTR_MASK (sizeof(long) - 1) 51 52 #define TESTBYTE \ 53 do { \ 54 if (*p != (unsigned char)c) \ 55 goto done; \ 56 p++; \ 57 } while (0) 58 59 void * 60 memcchr(const void *begin, int c, size_t n) 61 { 62 const unsigned long *lp; 63 const unsigned char *p, *end; 64 unsigned long word; 65 66 /* Four or eight repetitions of `c'. */ 67 word = (unsigned char)c; 68 word |= word << 8; 69 word |= word << 16; 70 #if LONG_BIT >= 64 71 word |= word << 32; 72 #endif 73 74 /* Don't perform memory I/O when passing a zero-length buffer. */ 75 if (n == 0) 76 return (NULL); 77 78 /* 79 * First determine whether there is a character unequal to `c' 80 * in the first word. As this word may contain bytes before 81 * `begin', we may execute this loop spuriously. 82 */ 83 lp = (const unsigned long *)((uintptr_t)begin & ~LONGPTR_MASK); 84 end = (const unsigned char *)begin + n; 85 if (*lp++ != word) 86 for (p = begin; p < (const unsigned char *)lp;) 87 TESTBYTE; 88 89 /* Now compare the data one word at a time. */ 90 for (; (const unsigned char *)lp < end; lp++) { 91 if (*lp != word) { 92 p = (const unsigned char *)lp; 93 TESTBYTE; 94 TESTBYTE; 95 TESTBYTE; 96 #if LONG_BIT >= 64 97 TESTBYTE; 98 TESTBYTE; 99 TESTBYTE; 100 TESTBYTE; 101 #endif 102 goto done; 103 } 104 } 105 106 return (NULL); 107 108 done: 109 /* 110 * If the end of the buffer is not word aligned, the previous 111 * loops may obtain an address that's beyond the end of the 112 * buffer. 113 */ 114 if (p < end) 115 return (__DECONST(void *, p)); 116 return (NULL); 117 } 118