130 lines
3.7 KiB
C
130 lines
3.7 KiB
C
/*-
|
|
* Copyright (c) 2009, 2010 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("$FreeBSD$");
|
|
|
|
#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);
|
|
}
|