-/* Copyright (C) 1994, 1999, 2002-2003, 2005-2006 Free Software Foundation, Inc.
-This file is part of the GNU C Library.
-
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation; either version 2, or (at your option)
-any later version.
-
-This program 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 General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software Foundation,
-Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, 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 */
+/* c-strstr.c -- substring search in C locale
+ Copyright (C) 2005-2007 Free Software Foundation, Inc.
+ Written by Bruno Haible <bruno@clisp.org>, 2005, 2007.
-#include <config.h>
-
-#include <string.h>
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2, or (at your option)
+ any later version.
-typedef unsigned chartype;
+ This program 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 General Public License for more details.
-char *
-c_strstr (const char *phaystack, const char *pneedle)
-{
- register const unsigned char *haystack, *needle;
- register chartype b, c;
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software Foundation,
+ Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
- haystack = (const unsigned char *) phaystack;
- needle = (const unsigned char *) pneedle;
+#include <config.h>
- b = *needle;
- if (b != '\0')
- {
- haystack--; /* possible ANSI violation */
- do
- {
- c = *++haystack;
- if (c == '\0')
- goto ret0;
- }
- while (c != b);
+/* Specification. */
+#include "c-strstr.h"
- c = *++needle;
- if (c == '\0')
- goto foundneedle;
- ++needle;
- goto jin;
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
- for (;;)
- {
- register chartype a;
- register const unsigned char *rhaystack, *rneedle;
+#include "allocsa.h"
- do
- {
- a = *++haystack;
- if (a == '\0')
- goto ret0;
- if (a == b)
+/* Knuth-Morris-Pratt algorithm.
+ See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
+ Return a boolean indicating success. */
+static bool
+knuth_morris_pratt (const char *haystack, const char *needle,
+ const char **resultp)
+{
+ size_t m = strlen (needle);
+
+ /* Allocate the table. */
+ size_t *table = (size_t *) allocsa (m * sizeof (size_t));
+ if (table == NULL)
+ return false;
+ /* Fill the table.
+ For 0 < i < m:
+ 0 < table[i] <= i is defined such that
+ rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i]
+ implies
+ forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1],
+ and table[i] is as large as possible with this property.
+ table[0] remains uninitialized. */
+ {
+ size_t i, j;
+
+ table[1] = 1;
+ j = 0;
+ for (i = 2; i < m; i++)
+ {
+ unsigned char b = (unsigned char) needle[i - 1];
+
+ for (;;)
+ {
+ if (b == (unsigned char) needle[j])
+ {
+ table[i] = i - ++j;
break;
- a = *++haystack;
- if (a == '\0')
- goto ret0;
-shloop:; }
- while (a != b);
-
-jin: a = *++haystack;
- if (a == '\0')
- goto ret0;
-
- if (a != c)
- goto shloop;
-
- rhaystack = haystack-- + 1;
- rneedle = needle;
- a = *rneedle;
-
- if (*rhaystack == a)
- do
+ }
+ if (j == 0)
{
- if (a == '\0')
- goto foundneedle;
- ++rhaystack;
- a = *++needle;
- if (*rhaystack != a)
- break;
- if (a == '\0')
- goto foundneedle;
- ++rhaystack;
- a = *++needle;
+ table[i] = i;
+ break;
}
- while (*rhaystack == a);
+ j = j - table[j];
+ }
+ }
+ }
+
+ /* Search, using the table to accelerate the processing. */
+ {
+ size_t j;
+ const char *rhaystack;
+ const char *phaystack;
+
+ *resultp = NULL;
+ j = 0;
+ rhaystack = haystack;
+ phaystack = haystack;
+ /* Invariant: phaystack = rhaystack + j. */
+ while (*phaystack != '\0')
+ if ((unsigned char) needle[j] == (unsigned char) *phaystack)
+ {
+ j++;
+ phaystack++;
+ if (j == m)
+ {
+ /* The entire needle has been found. */
+ *resultp = rhaystack;
+ break;
+ }
+ }
+ else if (j > 0)
+ {
+ /* Found a match of needle[0..j-1], mismatch at needle[j]. */
+ rhaystack += table[j];
+ j -= table[j];
+ }
+ else
+ {
+ /* Found a mismatch at needle[0] already. */
+ rhaystack++;
+ phaystack++;
+ }
+ }
- needle = rneedle; /* took the register-poor approach */
+ freesa (table);
+ return true;
+}
- if (a == '\0')
- break;
- }
+/* Find the first occurrence of NEEDLE in HAYSTACK. */
+char *
+c_strstr (const char *haystack, const char *needle)
+{
+ /* Be careful not to look at the entire extent of haystack or needle
+ until needed. This is useful because of these two cases:
+ - haystack may be very long, and a match of needle found early,
+ - needle may be very long, and not even a short initial segment of
+ needle may be found in haystack. */
+ if (*needle != '\0')
+ {
+ /* Minimizing the worst-case complexity:
+ Let n = strlen(haystack), m = strlen(needle).
+ The naïve algorithm is O(n*m) worst-case.
+ The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
+ memory allocation.
+ To achieve linear complexity and yet amortize the cost of the memory
+ allocation, we activate the Knuth-Morris-Pratt algorithm only once
+ the naïve algorithm has already run for some time; more precisely,
+ when
+ - the outer loop count is >= 10,
+ - the average number of comparisons per outer loop is >= 5,
+ - the total number of comparisons is >= m.
+ But we try it only once. If the memory allocation attempt failed,
+ we don't retry it. */
+ bool try_kmp = true;
+ size_t outer_loop_count = 0;
+ size_t comparison_count = 0;
+ size_t last_ccount = 0; /* last comparison count */
+ const char *needle_last_ccount = needle; /* = needle + last_ccount */
+
+ /* Speed up the following searches of needle by caching its first
+ character. */
+ unsigned char b = (unsigned char) *needle;
+
+ needle++;
+ for (;; haystack++)
+ {
+ if (*haystack == '\0')
+ /* No match. */
+ return NULL;
+
+ /* See whether it's advisable to use an asymptotically faster
+ algorithm. */
+ if (try_kmp
+ && outer_loop_count >= 10
+ && comparison_count >= 5 * outer_loop_count)
+ {
+ /* See if needle + comparison_count now reaches the end of
+ needle. */
+ if (needle_last_ccount != NULL)
+ {
+ needle_last_ccount +=
+ strnlen (needle_last_ccount, comparison_count - last_ccount);
+ if (*needle_last_ccount == '\0')
+ needle_last_ccount = NULL;
+ last_ccount = comparison_count;
+ }
+ if (needle_last_ccount == NULL)
+ {
+ /* Try the Knuth-Morris-Pratt algorithm. */
+ const char *result;
+ bool success =
+ knuth_morris_pratt (haystack, needle - 1, &result);
+ if (success)
+ return (char *) result;
+ try_kmp = false;
+ }
+ }
+
+ outer_loop_count++;
+ comparison_count++;
+ if ((unsigned char) *haystack == b)
+ /* The first character matches. */
+ {
+ const char *rhaystack = haystack + 1;
+ const char *rneedle = needle;
+
+ for (;; rhaystack++, rneedle++)
+ {
+ if (*rneedle == '\0')
+ /* Found a match. */
+ return (char *) haystack;
+ if (*rhaystack == '\0')
+ /* No match. */
+ return NULL;
+ comparison_count++;
+ if ((unsigned char) *rhaystack != (unsigned char) *rneedle)
+ /* Nothing in this round. */
+ break;
+ }
+ }
+ }
}
-foundneedle:
- return (char *) haystack;
-ret0:
- return 0;
+ else
+ return (char *) haystack;
}
projects / gnulib.git / blobdiff