2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2009, 2010 Xin LI <delphij@FreeBSD.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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
28 #include <sys/cdefs.h>
29 __FBSDID("$FreeBSD$");
31 #include <sys/libkern.h>
32 #include <sys/limits.h>
35 * Portable strlen() for 32-bit and 64-bit systems.
39 * ((x - 0x01....01) & ~x & 0x80....80)
41 * would evaluate to a non-zero value iff any of the bytes in the
42 * original word is zero.
44 * The algorithm above is found on "Hacker's Delight" by
45 * Henry S. Warren, Jr.
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.
52 /* Magic numbers for the algorithm */
54 static const unsigned long mask01 = 0x01010101;
55 static const unsigned long mask80 = 0x80808080;
57 static const unsigned long mask01 = 0x0101010101010101;
58 static const unsigned long mask80 = 0x8080808080808080;
60 #error Unsupported word size
63 #define LONGPTR_MASK (sizeof(long) - 1)
66 * Helper macro to return string length if we caught the zero
72 return (p - str + x); \
76 (strlen)(const char *str)
79 const unsigned long *lp;
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
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.
92 lp = (const unsigned long *)((uintptr_t)str & ~LONGPTR_MASK);
94 vb = ((~*lp) & mask80);
97 /* Check if we have \0 in the first part */
98 for (p = str; p < (const char *)lp; p++)
102 /* Scan the rest of the string using word sized operation */
105 vb = ((~*lp) & mask80);
107 p = (const char *)(lp);