mirror of
https://sourceware.org/git/glibc.git
synced 2025-07-28 00:21:52 +03:00
* string/Makefile (distribute): Add str-two-way.h.
2008-03-29 Eric Blake <ebb9@byu.net> Rewrite string searches to O(n) rather than O(n^2). * string/str-two-way.h: New file. For linear fixed-allocation string searching. * string/memmem.c: New implementation. * string/strstr.c: New implementation. * string/strcasestr.c: New implementation. * sysdeps/posix/getaddrinfo.c (getaddrinfo): Call _res_hconf_init
This commit is contained in:
Ulrich Drepper
142
string/strstr.c
142
string/strstr.c
@ -1,5 +1,5 @@
|
||||
/* Return the offset of one string within another.
|
||||
Copyright (C) 1994,1996,1997,2000,2001,2003 Free Software Foundation, Inc.
|
||||
Copyright (C) 1994,1996,1997,2000,2001,2003,2008 Free Software Foundation, Inc.
|
||||
This file is part of the GNU C Library.
|
||||
|
||||
The GNU C Library is free software; you can redistribute it and/or
|
||||
@ -17,107 +17,71 @@
|
||||
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
|
||||
02111-1307 USA. */
|
||||
|
||||
/*
|
||||
* My personal strstr() implementation that beats most other algorithms.
|
||||
* Until someone tells me otherwise, I assume that this is the
|
||||
* fastest implementation of strstr() in C.
|
||||
* I deliberately chose not to comment it. You should have at least
|
||||
* as much fun trying to understand it, as I had to write it :-).
|
||||
*
|
||||
* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
|
||||
/* This particular implementation was written by Eric Blake, 2008. */
|
||||
|
||||
#if HAVE_CONFIG_H
|
||||
#ifndef _LIBC
|
||||
# include <config.h>
|
||||
#endif
|
||||
|
||||
#if defined _LIBC || defined HAVE_STRING_H
|
||||
# include <string.h>
|
||||
/* Specification of strstr. */
|
||||
#include <string.h>
|
||||
|
||||
#include <stdbool.h>
|
||||
|
||||
#ifndef _LIBC
|
||||
# define __builtin_expect(expr, val) (expr)
|
||||
#endif
|
||||
|
||||
typedef unsigned chartype;
|
||||
#define RETURN_TYPE char *
|
||||
#define AVAILABLE(h, h_l, j, n_l) \
|
||||
(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
|
||||
&& ((h_l) = (j) + (n_l)))
|
||||
#include "str-two-way.h"
|
||||
|
||||
#undef strstr
|
||||
|
||||
/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
|
||||
if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
|
||||
HAYSTACK. */
|
||||
char *
|
||||
strstr (phaystack, pneedle)
|
||||
const char *phaystack;
|
||||
const char *pneedle;
|
||||
strstr (const char *haystack_start, const char *needle_start)
|
||||
{
|
||||
const unsigned char *haystack, *needle;
|
||||
chartype b;
|
||||
const unsigned char *rneedle;
|
||||
const char *haystack = haystack_start;
|
||||
const char *needle = needle_start;
|
||||
size_t needle_len; /* Length of NEEDLE. */
|
||||
size_t haystack_len; /* Known minimum length of HAYSTACK. */
|
||||
bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
|
||||
|
||||
haystack = (const unsigned char *) phaystack;
|
||||
/* Determine length of NEEDLE, and in the process, make sure
|
||||
HAYSTACK is at least as long (no point processing all of a long
|
||||
NEEDLE if HAYSTACK is too short). */
|
||||
while (*haystack && *needle)
|
||||
ok &= *haystack++ == *needle++;
|
||||
if (*needle)
|
||||
return NULL;
|
||||
if (ok)
|
||||
return (char *) haystack_start;
|
||||
|
||||
if ((b = *(needle = (const unsigned char *) pneedle)))
|
||||
{
|
||||
chartype c;
|
||||
haystack--; /* possible ANSI violation */
|
||||
/* Reduce the size of haystack using strchr, since it has a smaller
|
||||
linear coefficient than the Two-Way algorithm. */
|
||||
needle_len = needle - needle_start;
|
||||
haystack = strchr (haystack_start + 1, *needle_start);
|
||||
if (!haystack || __builtin_expect (needle_len == 1, 0))
|
||||
return (char *) haystack;
|
||||
needle -= needle_len;
|
||||
haystack_len = (haystack > haystack_start + needle_len ? 1
|
||||
: needle_len + haystack_start - haystack);
|
||||
|
||||
{
|
||||
chartype a;
|
||||
do
|
||||
if (!(a = *++haystack))
|
||||
goto ret0;
|
||||
while (a != b);
|
||||
}
|
||||
|
||||
if (!(c = *++needle))
|
||||
goto foundneedle;
|
||||
++needle;
|
||||
goto jin;
|
||||
|
||||
for (;;)
|
||||
{
|
||||
{
|
||||
chartype a;
|
||||
if (0)
|
||||
jin:{
|
||||
if ((a = *++haystack) == c)
|
||||
goto crest;
|
||||
}
|
||||
else
|
||||
a = *++haystack;
|
||||
do
|
||||
{
|
||||
for (; a != b; a = *++haystack)
|
||||
{
|
||||
if (!a)
|
||||
goto ret0;
|
||||
if ((a = *++haystack) == b)
|
||||
break;
|
||||
if (!a)
|
||||
goto ret0;
|
||||
}
|
||||
}
|
||||
while ((a = *++haystack) != c);
|
||||
}
|
||||
crest:
|
||||
{
|
||||
chartype a;
|
||||
{
|
||||
const unsigned char *rhaystack;
|
||||
if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
|
||||
do
|
||||
{
|
||||
if (!a)
|
||||
goto foundneedle;
|
||||
if (*++rhaystack != (a = *++needle))
|
||||
break;
|
||||
if (!a)
|
||||
goto foundneedle;
|
||||
}
|
||||
while (*++rhaystack == (a = *++needle));
|
||||
needle = rneedle; /* took the register-poor aproach */
|
||||
}
|
||||
if (!a)
|
||||
break;
|
||||
}
|
||||
}
|
||||
}
|
||||
foundneedle:
|
||||
return (char *) haystack;
|
||||
ret0:
|
||||
return 0;
|
||||
/* Perform the search. Abstract memory is considered to be an array
|
||||
of 'unsigned char' values, not an array of 'char' values. See
|
||||
ISO C 99 section 6.2.6.1. */
|
||||
if (needle_len < LONG_NEEDLE_THRESHOLD)
|
||||
return two_way_short_needle ((const unsigned char *) haystack,
|
||||
haystack_len,
|
||||
(const unsigned char *) needle, needle_len);
|
||||
return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
|
||||
(const unsigned char *) needle, needle_len);
|
||||
}
|
||||
libc_hidden_builtin_def (strstr)
|
||||
|
||||
#undef LONG_NEEDLE_THRESHOLD
|
||||
|
||||
Reference in New Issue
Block a user