mirror of
https://sourceware.org/git/glibc.git
synced 2025-11-03 20:53:13 +03:00
110 lines
3.4 KiB
C
110 lines
3.4 KiB
C
/* Copyright (C) 1991-2017 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Written by Torbjorn Granlund (tege@sics.se),
|
|
with help from Dan Sahlin (dan@sics.se);
|
|
commentary by Jim Blandy (jimb@ai.mit.edu).
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <string.h>
|
|
#include <stdlib.h>
|
|
|
|
#undef strlen
|
|
|
|
#ifndef STRLEN
|
|
# define STRLEN strlen
|
|
#endif
|
|
|
|
/* Return the length of the null-terminated string STR. Scan for
|
|
the null terminator quickly by testing four bytes at a time. */
|
|
size_t
|
|
STRLEN (const char *str)
|
|
{
|
|
const char *char_ptr;
|
|
const unsigned long int *longword_ptr;
|
|
unsigned long int longword, himagic, lomagic;
|
|
|
|
/* Handle the first few characters by reading one character at a time.
|
|
Do this until CHAR_PTR is aligned on a longword boundary. */
|
|
for (char_ptr = str; ((unsigned long int) char_ptr
|
|
& (sizeof (longword) - 1)) != 0;
|
|
++char_ptr)
|
|
if (*char_ptr == '\0')
|
|
return char_ptr - str;
|
|
|
|
/* All these elucidatory comments refer to 4-byte longwords,
|
|
but the theory applies equally well to 8-byte longwords. */
|
|
|
|
longword_ptr = (unsigned long int *) char_ptr;
|
|
|
|
/* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
|
|
the "holes." Note that there is a hole just to the left of
|
|
each byte, with an extra at the end:
|
|
|
|
bits: 01111110 11111110 11111110 11111111
|
|
bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
|
|
|
|
The 1-bits make sure that carries propagate to the next 0-bit.
|
|
The 0-bits provide holes for carries to fall into. */
|
|
himagic = 0x80808080L;
|
|
lomagic = 0x01010101L;
|
|
if (sizeof (longword) > 4)
|
|
{
|
|
/* 64-bit version of the magic. */
|
|
/* Do the shift in two steps to avoid a warning if long has 32 bits. */
|
|
himagic = ((himagic << 16) << 16) | himagic;
|
|
lomagic = ((lomagic << 16) << 16) | lomagic;
|
|
}
|
|
if (sizeof (longword) > 8)
|
|
abort ();
|
|
|
|
/* Instead of the traditional loop which tests each character,
|
|
we will test a longword at a time. The tricky part is testing
|
|
if *any of the four* bytes in the longword in question are zero. */
|
|
for (;;)
|
|
{
|
|
longword = *longword_ptr++;
|
|
|
|
if (((longword - lomagic) & ~longword & himagic) != 0)
|
|
{
|
|
/* Which of the bytes was the zero? If none of them were, it was
|
|
a misfire; continue the search. */
|
|
|
|
const char *cp = (const char *) (longword_ptr - 1);
|
|
|
|
if (cp[0] == 0)
|
|
return cp - str;
|
|
if (cp[1] == 0)
|
|
return cp - str + 1;
|
|
if (cp[2] == 0)
|
|
return cp - str + 2;
|
|
if (cp[3] == 0)
|
|
return cp - str + 3;
|
|
if (sizeof (longword) > 4)
|
|
{
|
|
if (cp[4] == 0)
|
|
return cp - str + 4;
|
|
if (cp[5] == 0)
|
|
return cp - str + 5;
|
|
if (cp[6] == 0)
|
|
return cp - str + 6;
|
|
if (cp[7] == 0)
|
|
return cp - str + 7;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
libc_hidden_builtin_def (strlen)
|