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/limits.h> 32 #include <sys/types.h> 33 #include <string.h> 34 35 /* 36 * Portable strlen() for 32-bit and 64-bit systems. 37 * 38 * The expression: 39 * 40 * ((x - 0x01....01) & ~x & 0x80....80) 41 * 42 * would evaluate to a non-zero value iff any of the bytes in the 43 * original word is zero. 44 * 45 * The algorithm above is found on "Hacker's Delight" by 46 * Henry S. Warren, Jr. 47 * 48 * Note: this leaves performance on the table and each architecture 49 * would be best served with a tailor made routine instead. 50 */ 51 52 #if LONG_BIT == 32 53 static const unsigned long mask01 = 0x01010101; 54 static const unsigned long mask80 = 0x80808080; 55 #elif LONG_BIT == 64 56 static const unsigned long mask01 = 0x0101010101010101; 57 static const unsigned long mask80 = 0x8080808080808080; 58 #else 59 #error Unsupported word size 60 #endif 61 62 #define LONGPTR_MASK (sizeof(long) - 1) 63 64 #if BYTE_ORDER == LITTLE_ENDIAN 65 #define FINDZERO __builtin_ctzl 66 #else 67 #define FINDZERO __builtin_clzl 68 #endif 69 70 size_t 71 strlen(const char *str) 72 { 73 const unsigned long *lp; 74 unsigned long mask; 75 long va, vb; 76 long val; 77 78 lp = (unsigned long *) (uintptr_t) str; 79 if ((uintptr_t)lp & LONGPTR_MASK) { 80 lp = (__typeof(lp)) ((uintptr_t)lp & ~LONGPTR_MASK); 81 #if BYTE_ORDER == LITTLE_ENDIAN 82 mask = ~(~0UL << (((uintptr_t)str & LONGPTR_MASK) << 3)); 83 #else 84 mask = ~(~0UL >> (((uintptr_t)str & LONGPTR_MASK) << 3)); 85 #endif 86 val = *lp | mask; 87 va = (val - mask01); 88 vb = ((~val) & mask80); 89 if (va & vb) { 90 return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); 91 } 92 lp++; 93 } 94 95 for (; ; lp++) { 96 va = (*lp - mask01); 97 vb = ((~*lp) & mask80); 98 if (va & vb) { 99 return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); 100 } 101 } 102 103 __builtin_unreachable(); 104 return (0); 105 } 106