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Imported Upstream version 1.4.16+git20130902

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Jan Wagner 2013-11-26 23:59:47 +01:00
parent e76be63abf
commit e70fb8c051
517 changed files with 44015 additions and 43295 deletions
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65
gl/str-two-way.h
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@ -1,5 +1,5 @@
/* Byte-wise substring search, using the Two-Way algorithm.
Copyright (C) 2008, 2009, 2010 Free Software Foundation, Inc.
Copyright (C) 2008-2013 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Written by Eric Blake <ebb9@byu.net>, 2008.
@ -14,8 +14,7 @@
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/>. */
/* Before including this file, you need to include <config.h> and
<string.h>, and define:
@ -44,14 +43,15 @@
#include <limits.h>
#include <stdint.h>
/* We use the Two-Way string matching algorithm, which guarantees
linear complexity with constant space. Additionally, for long
needles, we also use a bad character shift table similar to the
Boyer-Moore algorithm to achieve improved (potentially sub-linear)
performance.
/* We use the Two-Way string matching algorithm (also known as
Chrochemore-Perrin), which guarantees linear complexity with
constant space. Additionally, for long needles, we also use a bad
character shift table similar to the Boyer-Moore algorithm to
achieve improved (potentially sub-linear) performance.
See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260,
http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm,
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.34.6641&rep=rep1&type=pdf
*/
/* Point at which computing a bad-byte shift table is likely to be
@ -95,11 +95,14 @@
A critical factorization has the property that the local period
equals the global period. All strings have at least one critical
factorization with the left half smaller than the global period.
And while some strings have more than one critical factorization,
it is provable that with an ordered alphabet, at least one of the
critical factorizations corresponds to a maximal suffix.
Given an ordered alphabet, a critical factorization can be computed
in linear time, with 2 * NEEDLE_LEN comparisons, by computing the
larger of two ordered maximal suffixes. The ordered maximal
suffixes are determined by lexicographic comparison of
shorter of two ordered maximal suffixes. The ordered maximal
suffixes are determined by lexicographic comparison while tracking
periodicity. */
static size_t
critical_factorization (const unsigned char *needle, size_t needle_len,
@ -112,6 +115,14 @@ critical_factorization (const unsigned char *needle, size_t needle_len,
size_t p; /* Intermediate period. */
unsigned char a, b; /* Current comparison bytes. */
/* Special case NEEDLE_LEN of 1 or 2 (all callers already filtered
out 0-length needles. */
if (needle_len < 3)
{
*period = 1;
return needle_len - 1;
}
/* Invariants:
0 <= j < NEEDLE_LEN - 1
-1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
@ -190,8 +201,20 @@ critical_factorization (const unsigned char *needle, size_t needle_len,
}
}
/* Choose the longer suffix. Return the first byte of the right
half, rather than the last byte of the left half. */
/* Choose the shorter suffix. Return the index of the first byte of
the right half, rather than the last byte of the left half.
For some examples, 'banana' has two critical factorizations, both
exposed by the two lexicographic extreme suffixes of 'anana' and
'nana', where both suffixes have a period of 2. On the other
hand, with 'aab' and 'bba', both strings have a single critical
factorization of the last byte, with the suffix having a period
of 1. While the maximal lexicographic suffix of 'aab' is 'b',
the maximal lexicographic suffix of 'bba' is 'ba', which is not a
critical factorization. Conversely, the maximal reverse
lexicographic suffix of 'a' works for 'bba', but not 'ab' for
'aab'. The shorter suffix of the two will always be a critical
factorization. */
if (max_suffix_rev + 1 < max_suffix + 1)
return max_suffix + 1;
*period = p;
@ -226,9 +249,9 @@ two_way_short_needle (const unsigned char *haystack, size_t haystack_len,
first. */
if (CMP_FUNC (needle, needle + period, suffix) == 0)
{
/* Entire needle is periodic; a mismatch can only advance by the
period, so use memory to avoid rescanning known occurrences
of the period. */
/* Entire needle is periodic; a mismatch in the left half can
only advance by the period, so use memory to avoid rescanning
known occurrences of the period in the right half. */
size_t memory = 0;
j = 0;
while (AVAILABLE (haystack, haystack_len, j, needle_len))
@ -330,9 +353,9 @@ two_way_long_needle (const unsigned char *haystack, size_t haystack_len,
first. */
if (CMP_FUNC (needle, needle + period, suffix) == 0)
{
/* Entire needle is periodic; a mismatch can only advance by the
period, so use memory to avoid rescanning known occurrences
of the period. */
/* Entire needle is periodic; a mismatch in the left half can
only advance by the period, so use memory to avoid rescanning
known occurrences of the period in the right half. */
size_t memory = 0;
size_t shift;
j = 0;
@ -349,8 +372,8 @@ two_way_long_needle (const unsigned char *haystack, size_t haystack_len,
a byte out of place, there can be no match until
after the mismatch. */
shift = needle_len - period;
memory = 0;
}
memory = 0;
j += shift;
continue;
}