pmt: initial 3.0.2 update
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161
include/libgnulib/str-kmp.h
Executable file
161
include/libgnulib/str-kmp.h
Executable file
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/* Substring search in a NUL terminated string of UNIT elements,
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using the Knuth-Morris-Pratt algorithm.
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Copyright (C) 2005-2024 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2005.
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This file is free software.
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It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".
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You can redistribute it and/or modify it under either
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- the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation, either version 3, or (at your
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option) any later version, or
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- the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2, or (at your option)
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any later version, or
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- the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
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This file 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 GNU
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Lesser General Public License and the GNU General Public License
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for more details.
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You should have received a copy of the GNU Lesser General Public
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License and of the GNU General Public License along with this
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program. If not, see <https://www.gnu.org/licenses/>. */
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/* Before including this file, you need to define:
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UNIT The element type of the needle and haystack.
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CANON_ELEMENT(c) A macro that canonicalizes an element right after
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it has been fetched from needle or haystack.
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The argument is of type UNIT; the result must be
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of type UNIT as well. */
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/* Knuth-Morris-Pratt algorithm.
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See https://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
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HAYSTACK is the NUL terminated string in which to search for.
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NEEDLE is the string to search for in HAYSTACK, consisting of NEEDLE_LEN
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units.
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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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static bool
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knuth_morris_pratt (const UNIT *haystack,
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const UNIT *needle, size_t needle_len,
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const UNIT **resultp)
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{
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size_t m = needle_len;
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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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if (table == NULL)
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return false;
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/* Fill the table.
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For 0 < i < m:
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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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This implies:
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1) For 0 < i < m:
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If table[i] < i,
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needle[table[i]..i-1] = needle[0..i-1-table[i]].
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2) For 0 < i < m:
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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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implies
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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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{
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size_t i, j;
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/* i = 1: Nothing to verify for x = 0. */
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table[1] = 1;
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j = 0;
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for (i = 2; i < m; i++)
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{
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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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UNIT b = CANON_ELEMENT (needle[i - 1]);
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for (;;)
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{
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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 (needle[j]))
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{
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/* Set table[i] := i-1-j. */
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table[i] = i - ++j;
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break;
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}
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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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if (j == 0)
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{
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/* The inequality holds for all possible x. */
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table[i] = i;
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break;
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}
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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-2]
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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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= needle[0..i-2-x],
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hence needle[x..i-1] != needle[0..i-1-x].
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Furthermore
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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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j = j - table[j];
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}
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/* Here: j = i - table[i]. */
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}
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}
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/* Search, using the table to accelerate the processing. */
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{
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size_t j;
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const UNIT *rhaystack;
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const UNIT *phaystack;
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*resultp = NULL;
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j = 0;
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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 (needle[j]) == CANON_ELEMENT (*phaystack))
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{
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j++;
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phaystack++;
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if (j == m)
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{
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/* The entire needle has been found. */
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*resultp = rhaystack;
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break;
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}
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}
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else if (j > 0)
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{
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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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j -= table[j];
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}
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else
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{
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/* Found a mismatch at needle[0] already. */
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rhaystack++;
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phaystack++;
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}
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}
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freea (table);
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return true;
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}
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#undef CANON_ELEMENT
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