1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2009, 2010 Xin LI <delphij@FreeBSD.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 */ 27 28 #include <sys/cdefs.h> 29 __FBSDID("$FreeBSD$"); 30 31 #include <sys/libkern.h> 32 #include <sys/limits.h> 33 34 /* 35 * Portable strlen() for 32-bit and 64-bit systems. 36 * 37 * The expression: 38 * 39 * ((x - 0x01....01) & ~x & 0x80....80) 40 * 41 * would evaluate to a non-zero value iff any of the bytes in the 42 * original word is zero. 43 * 44 * The algorithm above is found on "Hacker's Delight" by 45 * Henry S. Warren, Jr. 46 * 47 * Note: this leaves performance on the table and each architecture 48 * would be best served with a tailor made routine instead, even if 49 * using the same trick. 50 */ 51 52 /* Magic numbers for the algorithm */ 53 #if LONG_BIT == 32 54 static const unsigned long mask01 = 0x01010101; 55 static const unsigned long mask80 = 0x80808080; 56 #elif LONG_BIT == 64 57 static const unsigned long mask01 = 0x0101010101010101; 58 static const unsigned long mask80 = 0x8080808080808080; 59 #else 60 #error Unsupported word size 61 #endif 62 63 #define LONGPTR_MASK (sizeof(long) - 1) 64 65 /* 66 * Helper macro to return string length if we caught the zero 67 * byte. 68 */ 69 #define testbyte(x) \ 70 do { \ 71 if (p[x] == '\0') \ 72 return (p - str + x); \ 73 } while (0) 74 75 size_t 76 (strlen)(const char *str) 77 { 78 const char *p; 79 const unsigned long *lp; 80 long va, vb; 81 82 /* 83 * Before trying the hard (unaligned byte-by-byte access) way 84 * to figure out whether there is a nul character, try to see 85 * if there is a nul character is within this accessible word 86 * first. 87 * 88 * p and (p & ~LONGPTR_MASK) must be equally accessible since 89 * they always fall in the same memory page, as long as page 90 * boundaries is integral multiple of word size. 91 */ 92 lp = (const unsigned long *)((uintptr_t)str & ~LONGPTR_MASK); 93 va = (*lp - mask01); 94 vb = ((~*lp) & mask80); 95 lp++; 96 if (va & vb) 97 /* Check if we have \0 in the first part */ 98 for (p = str; p < (const char *)lp; p++) 99 if (*p == '\0') 100 return (p - str); 101 102 /* Scan the rest of the string using word sized operation */ 103 for (; ; lp++) { 104 va = (*lp - mask01); 105 vb = ((~*lp) & mask80); 106 if (va & vb) { 107 p = (const char *)(lp); 108 testbyte(0); 109 testbyte(1); 110 testbyte(2); 111 testbyte(3); 112 #if (LONG_BIT >= 64) 113 testbyte(4); 114 testbyte(5); 115 testbyte(6); 116 testbyte(7); 117 #endif 118 } 119 } 120 121 /* NOTREACHED */ 122 return (0); 123 } 124