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- /*-
- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
- *
- * Copyright (c) 2009, 2010 Xin LI <delphij@FreeBSD.org>
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
- #include <sys/cdefs.h>
- __FBSDID("$FreeBSD$");
- #include <sys/libkern.h>
- #include <sys/limits.h>
- /*
- * Portable strlen() for 32-bit and 64-bit systems.
- *
- * Rationale: it is generally much more efficient to do word length
- * operations and avoid branches on modern computer systems, as
- * compared to byte-length operations with a lot of branches.
- *
- * The expression:
- *
- * ((x - 0x01....01) & ~x & 0x80....80)
- *
- * would evaluate to a non-zero value iff any of the bytes in the
- * original word is zero.
- *
- * On multi-issue processors, we can divide the above expression into:
- * a) (x - 0x01....01)
- * b) (~x & 0x80....80)
- * c) a & b
- *
- * Where, a) and b) can be partially computed in parallel.
- *
- * The algorithm above is found on "Hacker's Delight" by
- * Henry S. Warren, Jr.
- */
- /* Magic numbers for the algorithm */
- #if LONG_BIT == 32
- static const unsigned long mask01 = 0x01010101;
- static const unsigned long mask80 = 0x80808080;
- #elif LONG_BIT == 64
- static const unsigned long mask01 = 0x0101010101010101;
- static const unsigned long mask80 = 0x8080808080808080;
- #else
- #error Unsupported word size
- #endif
- #define LONGPTR_MASK (sizeof(long) - 1)
- /*
- * Helper macro to return string length if we caught the zero
- * byte.
- */
- #define testbyte(x) \
- do { \
- if (p[x] == '\0') \
- return (p - str + x); \
- } while (0)
- size_t
- (strlen)(const char *str)
- {
- const char *p;
- const unsigned long *lp;
- long va, vb;
- /*
- * Before trying the hard (unaligned byte-by-byte access) way
- * to figure out whether there is a nul character, try to see
- * if there is a nul character is within this accessible word
- * first.
- *
- * p and (p & ~LONGPTR_MASK) must be equally accessible since
- * they always fall in the same memory page, as long as page
- * boundaries is integral multiple of word size.
- */
- lp = (const unsigned long *)((uintptr_t)str & ~LONGPTR_MASK);
- va = (*lp - mask01);
- vb = ((~*lp) & mask80);
- lp++;
- if (va & vb)
- /* Check if we have \0 in the first part */
- for (p = str; p < (const char *)lp; p++)
- if (*p == '\0')
- return (p - str);
- /* Scan the rest of the string using word sized operation */
- for (; ; lp++) {
- va = (*lp - mask01);
- vb = ((~*lp) & mask80);
- if (va & vb) {
- p = (const char *)(lp);
- testbyte(0);
- testbyte(1);
- testbyte(2);
- testbyte(3);
- #if (LONG_BIT >= 64)
- testbyte(4);
- testbyte(5);
- testbyte(6);
- testbyte(7);
- #endif
- }
- }
- /* NOTREACHED */
- return (0);
- }
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