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/* Substring test for UTF-8/UTF-16/UTF-32 strings. -*- coding: utf-8 -*-
Copyright (C) 1999, 2002, 2006, 2010-2017 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2002, 2005.
This program is free software: you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published
by the Free Software Foundation; either version 3 of the License, 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
UNIT *
FUNC (const UNIT *haystack, const UNIT *needle)
{
UNIT first = needle[0];
/* Is needle empty? */
if (first == 0)
return (UNIT *) haystack;
/* Is needle nearly empty (only one unit)? */
if (needle[1] == 0)
return U_STRCHR (haystack, first);
#ifdef U_STRMBTOUC
/* Is needle nearly empty (only one character)? */
{
ucs4_t first_uc;
int count = U_STRMBTOUC (&first_uc, needle);
if (count > 0 && needle[count] == 0)
return U_STRCHR (haystack, first_uc);
}
#endif
#if UNIT_IS_UINT8_T
return (uint8_t *) strstr ((const char *) haystack, (const char *) needle);
#else
{
/* Minimizing the worst-case complexity:
Let n = U_STRLEN(haystack), m = U_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 UNIT *needle_last_ccount = needle; /* = needle + last_ccount */
/* Speed up the following searches of needle by caching its first
character. */
UNIT b = *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 +=
U_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 UNIT *result;
bool success =
knuth_morris_pratt (haystack,
needle - 1, U_STRLEN (needle - 1),
&result);
if (success)
return (UNIT *) result;
try_kmp = false;
}
}
outer_loop_count++;
comparison_count++;
if (*haystack == b)
/* The first character matches. */
{
const UNIT *rhaystack = haystack + 1;
const UNIT *rneedle = needle;
for (;; rhaystack++, rneedle++)
{
if (*rneedle == 0)
/* Found a match. */
return (UNIT *) haystack;
if (*rhaystack == 0)
/* No match. */
return NULL;
comparison_count++;
if (*rhaystack != *rneedle)
/* Nothing in this round. */
break;
}
}
}
}
#endif
}
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