-/* Copyright (C) 1991,92,93,94,96,97,98,2000,2004,2007 Free Software Foundation, Inc.
+/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2014 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
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. */
+ with this program; if not, see <http://www.gnu.org/licenses/>. */
+
+/* This particular implementation was written by Eric Blake, 2008. */
#ifndef _LIBC
# include <config.h>
#endif
-#include <stddef.h>
+/* Specification of memmem. */
#include <string.h>
-#include <stdbool.h>
-
-#include "malloca.h"
#ifndef _LIBC
# define __builtin_expect(expr, val) (expr)
#endif
-/* 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 *last_haystack,
- const char *needle, size_t m,
- const char **resultp)
-{
- /* Allocate the table. */
- size_t *table = (size_t *) malloca (m * sizeof (size_t));
- if (table == NULL)
- return false;
- /* Fill the table.
- For 0 < i < m:
- 0 < table[i] <= i is defined such that
- forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],
- and table[i] is as large as possible with this property.
- This implies:
- 1) For 0 < i < m:
- If table[i] < i,
- needle[table[i]..i-1] = needle[0..i-1-table[i]].
- 2) For 0 < i < m:
- rhaystack[0..i-1] == needle[0..i-1]
- and exists h, i <= h < m: rhaystack[h] != needle[h]
- implies
- forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].
- table[0] remains uninitialized. */
- {
- size_t i, j;
-
- /* i = 1: Nothing to verify for x = 0. */
- table[1] = 1;
- j = 0;
-
- for (i = 2; i < m; i++)
- {
- /* Here: j = i-1 - table[i-1].
- The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold
- for x < table[i-1], by induction.
- Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
- unsigned char b = (unsigned char) needle[i - 1];
-
- for (;;)
- {
- /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]
- is known to hold for x < i-1-j.
- Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
- if (b == (unsigned char) needle[j])
- {
- /* Set table[i] := i-1-j. */
- table[i] = i - ++j;
- break;
- }
- /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
- for x = i-1-j, because
- needle[i-1] != needle[j] = needle[i-1-x]. */
- if (j == 0)
- {
- /* The inequality holds for all possible x. */
- table[i] = i;
- break;
- }
- /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
- for i-1-j < x < i-1-j+table[j], because for these x:
- needle[x..i-2]
- = needle[x-(i-1-j)..j-1]
- != needle[0..j-1-(x-(i-1-j))] (by definition of table[j])
- = needle[0..i-2-x],
- hence needle[x..i-1] != needle[0..i-1-x].
- Furthermore
- needle[i-1-j+table[j]..i-2]
- = needle[table[j]..j-1]
- = needle[0..j-1-table[j]] (by definition of table[j]). */
- j = j - table[j];
- }
- /* Here: j = i - table[i]. */
- }
- }
-
- /* 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 != last_haystack)
- 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++;
- }
- }
-
- freea (table);
- return true;
-}
+#define RETURN_TYPE void *
+#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
+#include "str-two-way.h"
/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
HAYSTACK. */
void *
memmem (const void *haystack_start, size_t haystack_len,
- const void *needle_start, size_t needle_len)
+ const void *needle_start, size_t needle_len)
{
- /* Operating with void * is awkward. */
- const char *haystack = (const char *) haystack_start;
- const char *needle = (const char *) needle_start;
- const char *last_haystack = haystack + haystack_len;
- const char *last_needle = needle + needle_len;
+ /* 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. */
+ const unsigned char *haystack = (const unsigned char *) haystack_start;
+ const unsigned char *needle = (const unsigned char *) needle_start;
if (needle_len == 0)
/* The first occurrence of the empty string is deemed to occur at
if (__builtin_expect (haystack_len < needle_len, 0))
return NULL;
- /* Use optimizations in memchr when possible. */
- if (__builtin_expect (needle_len == 1, 0))
- return memchr (haystack, (unsigned char) *needle, haystack_len);
-
- /* Minimizing the worst-case complexity:
- Let n = haystack_len, m = needle_len.
- 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;
-
- /* Speed up the following searches of needle by caching its first
- byte. */
- char b = *needle++;
-
- for (;; haystack++)
- {
- if (haystack == last_haystack)
- /* 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 (comparison_count >= needle_len)
- {
- /* Try the Knuth-Morris-Pratt algorithm. */
- const char *result;
- if (knuth_morris_pratt (haystack, last_haystack,
- needle - 1, needle_len, &result))
- return (void *) result;
- try_kmp = false;
- }
- }
-
- outer_loop_count++;
- comparison_count++;
- if (*haystack == b)
- /* The first byte matches. */
- {
- const char *rhaystack = haystack + 1;
- const char *rneedle = needle;
-
- for (;; rhaystack++, rneedle++)
- {
- if (rneedle == last_needle)
- /* Found a match. */
- return (void *) haystack;
- if (rhaystack == last_haystack)
- /* No match. */
- return NULL;
- comparison_count++;
- if (*rhaystack != *rneedle)
- /* Nothing in this round. */
- break;
- }
- }
- }
- }
-
- return NULL;
+ /* Use optimizations in memchr when possible, to reduce the search
+ size of haystack using a linear algorithm with a smaller
+ coefficient. However, avoid memchr for long needles, since we
+ can often achieve sublinear performance. */
+ if (needle_len < LONG_NEEDLE_THRESHOLD)
+ {
+ haystack = memchr (haystack, *needle, haystack_len);
+ if (!haystack || __builtin_expect (needle_len == 1, 0))
+ return (void *) haystack;
+ haystack_len -= haystack - (const unsigned char *) haystack_start;
+ if (haystack_len < needle_len)
+ return NULL;
+ return two_way_short_needle (haystack, haystack_len, needle, needle_len);
+ }
+ else
+ return two_way_long_needle (haystack, haystack_len, needle, needle_len);
}
+
+#undef LONG_NEEDLE_THRESHOLD
projects / gnulib.git / blobdiff