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/* Substring search in a NUL terminated string of 'char' elements,
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using the Knuth-Morris-Pratt algorithm.
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Copyright (C) 2005-2010 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2005.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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/* Before including this file, you need to define:
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CANON_ELEMENT(c) A macro that canonicalizes an element right after
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it has been fetched from one of the two strings.
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The argument is an 'unsigned char'; the result
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must be an 'unsigned char' as well. */
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/* Knuth-Morris-Pratt algorithm.
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See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
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Return a boolean indicating success:
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Return true and set *RESULTP if the search was completed.
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Return false if it was aborted because not enough memory was available. */
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knuth_morris_pratt_unibyte (const char *haystack, const char *needle,
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size_t m = strlen (needle);
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/* Allocate the table. */
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size_t *table = (size_t *) nmalloca (m, sizeof (size_t));
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0 < table[i] <= i is defined such that
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forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],
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and table[i] is as large as possible with this property.
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needle[table[i]..i-1] = needle[0..i-1-table[i]].
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rhaystack[0..i-1] == needle[0..i-1]
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and exists h, i <= h < m: rhaystack[h] != needle[h]
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forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].
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table[0] remains uninitialized. */
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/* i = 1: Nothing to verify for x = 0. */
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for (i = 2; i < m; i++)
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/* Here: j = i-1 - table[i-1].
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The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold
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for x < table[i-1], by induction.
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Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
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unsigned char b = CANON_ELEMENT ((unsigned char) needle[i - 1]);
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/* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]
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is known to hold for x < i-1-j.
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Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
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if (b == CANON_ELEMENT ((unsigned char) needle[j]))
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/* Set table[i] := i-1-j. */
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/* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
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for x = i-1-j, because
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needle[i-1] != needle[j] = needle[i-1-x]. */
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/* The inequality holds for all possible x. */
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/* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
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for i-1-j < x < i-1-j+table[j], because for these x:
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= needle[x-(i-1-j)..j-1]
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!= needle[0..j-1-(x-(i-1-j))] (by definition of table[j])
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hence needle[x..i-1] != needle[0..i-1-x].
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needle[i-1-j+table[j]..i-2]
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= needle[table[j]..j-1]
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= needle[0..j-1-table[j]] (by definition of table[j]). */
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/* Here: j = i - table[i]. */
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/* Search, using the table to accelerate the processing. */
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const char *rhaystack;
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const char *phaystack;
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rhaystack = haystack;
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phaystack = haystack;
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/* Invariant: phaystack = rhaystack + j. */
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while (*phaystack != '\0')
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if (CANON_ELEMENT ((unsigned char) needle[j])
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== CANON_ELEMENT ((unsigned char) *phaystack))
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/* The entire needle has been found. */
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*resultp = rhaystack;
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/* Found a match of needle[0..j-1], mismatch at needle[j]. */
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rhaystack += table[j];
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/* Found a mismatch at needle[0] already. */