/* Case-insensitive searching in a string.
- Copyright (C) 2005-2006 Free Software Foundation, Inc.
+ Copyright (C) 2005-2007 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2005.
This program is free software; you can redistribute it and/or modify
#include <config.h>
/* Specification. */
-#include "strcasestr.h"
+#include <string.h>
#include <ctype.h>
-#include <stddef.h> /* for NULL */
+#include <stdbool.h>
+#include <stddef.h> /* for NULL, in case a nonstandard string.h lacks it */
-#if HAVE_MBRTOWC
-# include "mbuiter.h"
-#endif
+#include "allocsa.h"
#define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
+/* 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 = TOLOWER ((unsigned char) needle[i - 1]);
+
+ for (;;)
+ {
+ if (b == TOLOWER ((unsigned char) needle[j]))
+ {
+ table[i] = i - ++j;
+ break;
+ }
+ if (j == 0)
+ {
+ table[i] = i;
+ break;
+ }
+ 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 (TOLOWER ((unsigned char) needle[j])
+ == TOLOWER ((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++;
+ }
+ }
+
+ freesa (table);
+ return true;
+}
+
/* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
comparison.
Note: This function may, in multibyte locales, return success even if
char *
strcasestr (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 HAVE_MBRTOWC
- if (MB_CUR_MAX > 1)
+ if (*needle != '\0')
{
- mbui_iterator_t iter_needle;
-
- mbui_init (iter_needle, needle);
- if (mbui_avail (iter_needle))
+ /* 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 = TOLOWER ((unsigned char) *needle);
+
+ needle++;
+ for (;; haystack++)
{
- mbchar_t b;
- mbui_iterator_t iter_haystack;
-
- mb_copy (&b, &mbui_cur (iter_needle));
- if (b.wc_valid)
- b.wc = towlower (b.wc);
-
- mbui_init (iter_haystack, haystack);
- for (;; mbui_advance (iter_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)
{
- mbchar_t c;
-
- if (!mbui_avail (iter_haystack))
- /* No match. */
- return NULL;
-
- mb_copy (&c, &mbui_cur (iter_haystack));
- if (c.wc_valid)
- c.wc = towlower (c.wc);
- if (mb_equal (c, b))
- /* The first character matches. */
+ /* See if needle + comparison_count now reaches the end of
+ needle. */
+ if (needle_last_ccount != NULL)
{
- mbui_iterator_t rhaystack;
- mbui_iterator_t rneedle;
-
- memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
- mbui_advance (rhaystack);
-
- mbui_init (rneedle, needle);
- if (!mbui_avail (rneedle))
- abort ();
- mbui_advance (rneedle);
-
- for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
- {
- if (!mbui_avail (rneedle))
- /* Found a match. */
- return (char *) mbui_cur_ptr (iter_haystack);
- if (!mbui_avail (rhaystack))
- /* No match. */
- return NULL;
- if (!mb_caseequal (mbui_cur (rhaystack),
- mbui_cur (rneedle)))
- /* Nothing in this round. */
- break;
- }
+ 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;
}
}
- }
- else
- return (char *) haystack;
- }
- else
-#endif
- {
- if (*needle != '\0')
- {
- /* Speed up the following searches of needle by caching its first
- character. */
- unsigned char b = TOLOWER ((unsigned char) *needle);
- needle++;
- for (;; haystack++)
+ outer_loop_count++;
+ comparison_count++;
+ if (TOLOWER ((unsigned char) *haystack) == b)
+ /* The first character matches. */
{
- if (*haystack == '\0')
- /* No match. */
- return NULL;
- if (TOLOWER ((unsigned char) *haystack) == b)
- /* The first character matches. */
+ const char *rhaystack = haystack + 1;
+ const char *rneedle = needle;
+
+ for (;; rhaystack++, rneedle++)
{
- 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;
- if (TOLOWER ((unsigned char) *rhaystack)
- != TOLOWER ((unsigned char) *rneedle))
- /* Nothing in this round. */
- break;
- }
+ if (*rneedle == '\0')
+ /* Found a match. */
+ return (char *) haystack;
+ if (*rhaystack == '\0')
+ /* No match. */
+ return NULL;
+ comparison_count++;
+ if (TOLOWER ((unsigned char) *rhaystack)
+ != TOLOWER ((unsigned char) *rneedle))
+ /* Nothing in this round. */
+ break;
}
}
}
- else
- return (char *) haystack;
}
+ else
+ return (char *) haystack;
}
projects / gnulib.git / blobdiff