+++ /dev/null
-/*-
- * Copyright (c) 2009 Xin LI <delphij@FreeBSD.org>
- * All rights reserved.
- *
- * 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: src/lib/libc/string/strlen.c,v 1.7 2009/01/26 07:31:28 delphij Exp $");
-
-#include <limits.h>
-#include <sys/types.h>
-#include <string.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. However, we can further reduce ~1/3 of
- * time if we consider that strlen() usually operate on 7-bit ASCII
- * by employing the following expression, which allows false positive
- * when high bit of 1 and use the tail case to catch these case:
- *
- * ((x - 0x01....01) & 0x80....80)
- *
- * This is more than 5.2 times as fast as the raw implementation on
- * Intel T7300 under long mode for strings longer than word length.
- */
-
-/* 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;
-
- /* Skip the first few bytes until we have an aligned p */
- for (p = str; (uintptr_t)p & LONGPTR_MASK; p++)
- if (*p == '\0')
- return (p - str);
-
- /* Scan the rest of the string using word sized operation */
- for (lp = (const unsigned long *)p; ; lp++)
- if ((*lp - mask01) & mask80) {
- 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);
-}
-
projects / apple / libc.git / blobdiff