diff --git a/lib/libc/string/strlen.c b/lib/libc/string/strlen.c index a862ffc245ca..0bdc81d7bb9a 100644 --- a/lib/libc/string/strlen.c +++ b/lib/libc/string/strlen.c @@ -1,131 +1,105 @@ /*- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD * * Copyright (c) 2009, 2010 Xin LI * * 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 __FBSDID("$FreeBSD$"); #include #include #include /* * 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. + * + * Note: this leaves performance on the table and each architecture + * would be best served with a tailor made routine instead. */ -/* 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) +#if BYTE_ORDER == LITTLE_ENDIAN +#define FINDZERO __builtin_ctzl +#else +#define FINDZERO __builtin_clzl +#endif size_t strlen(const char *str) { - const char *p; const unsigned long *lp; + unsigned long mask; long va, vb; + long val; - /* - * 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); + lp = (unsigned long *) (uintptr_t) str; + if ((uintptr_t)lp & LONGPTR_MASK) { + lp = (__typeof(lp)) ((uintptr_t)lp & ~LONGPTR_MASK); +#if BYTE_ORDER == LITTLE_ENDIAN + mask = ~(~0UL << (((uintptr_t)str & LONGPTR_MASK) << 3)); +#else + mask = ~(~0UL >> (((uintptr_t)str & LONGPTR_MASK) << 3)); +#endif + val = *lp | mask; + va = (val - mask01); + vb = ((~val) & mask80); + if (va & vb) { + return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); + } + lp++; + } - /* 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 + return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); } } - /* NOTREACHED */ + __builtin_unreachable(); return (0); } diff --git a/sys/libkern/strlen.c b/sys/libkern/strlen.c index a8c7964f69a3..8fa5f3927ea9 100644 --- a/sys/libkern/strlen.c +++ b/sys/libkern/strlen.c @@ -1,130 +1,101 @@ /*- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD * * Copyright (c) 2009, 2010 Xin LI * * 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 __FBSDID("$FreeBSD$"); #include #include /* * 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) +#if BYTE_ORDER == LITTLE_ENDIAN +#define FINDZERO __builtin_ctzl +#else +#define FINDZERO __builtin_clzl +#endif size_t (strlen)(const char *str) { - const char *p; const unsigned long *lp; + unsigned long mask; long va, vb; + long val; - /* - * 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); + lp = (unsigned long *) (uintptr_t) str; + if ((uintptr_t)lp & LONGPTR_MASK) { + lp = (__typeof(lp)) ((uintptr_t)lp & ~LONGPTR_MASK); +#if BYTE_ORDER == LITTLE_ENDIAN + mask = ~(~0UL << (((uintptr_t)str & LONGPTR_MASK) << 3)); +#else + mask = ~(~0UL >> (((uintptr_t)str & LONGPTR_MASK) << 3)); +#endif + val = *lp | mask; + va = (val - mask01); + vb = ((~val) & mask80); + if (va & vb) { + return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); + } + lp++; + } - /* 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 + return ((const char *)lp - str + (FINDZERO(va & vb) >> 3)); } } - /* NOTREACHED */ + __builtin_unreachable(); return (0); }