#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.
-
- See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260
- and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
+/* 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,
+ 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
critical_factorization (const unsigned char *needle, size_t needle_len,
size_t *period)
{
- /* Index of last byte of left half. */
+ /* Index of last byte of left half, or SIZE_MAX. */
size_t max_suffix, max_suffix_rev;
size_t j; /* Index into NEEDLE for current candidate suffix. */
size_t k; /* Offset into current period. */
}
/* Invariants:
- 1 <= j < NEEDLE_LEN - 1
- 0 <= max_suffix{,_rev} < j
+ 0 <= j < NEEDLE_LEN - 1
+ -1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed)
min(max_suffix, max_suffix_rev) < global period of NEEDLE
1 <= p <= global period of NEEDLE
p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j]
*/
/* Perform lexicographic search. */
- max_suffix = 0;
- j = k = p = 1;
+ max_suffix = SIZE_MAX;
+ j = 0;
+ k = p = 1;
while (j + k < needle_len)
{
a = CANON_ELEMENT (needle[j + k]);
*period = p;
/* Perform reverse lexicographic search. */
- max_suffix_rev = 0;
- j = k = p = 1;
+ max_suffix_rev = SIZE_MAX;
+ j = 0;
+ k = p = 1;
while (j + k < needle_len)
{
a = CANON_ELEMENT (needle[j + k]);