diff options
Diffstat (limited to 'lib/unistr/u-strstr.h')
| -rw-r--r-- | lib/unistr/u-strstr.h | 116 |
1 files changed, 99 insertions, 17 deletions
diff --git a/lib/unistr/u-strstr.h b/lib/unistr/u-strstr.h index df32be8b..459215ec 100644 --- a/lib/unistr/u-strstr.h +++ b/lib/unistr/u-strstr.h @@ -1,6 +1,6 @@ /* Substring test for UTF-8/UTF-16/UTF-32 strings. - Copyright (C) 1999, 2002, 2006, 2009-2010 Free Software Foundation, Inc. - Written by Bruno Haible <bruno@clisp.org>, 2002. + Copyright (C) 1999, 2002, 2006, 2010-2015 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 @@ -24,26 +24,108 @@ FUNC (const UNIT *haystack, const UNIT *needle) if (first == 0) return (UNIT *) haystack; - /* Is needle nearly empty? */ + /* Is needle nearly empty (only one unit)? */ if (needle[1] == 0) return U_STRCHR (haystack, first); - /* Search for needle's first unit. */ - for (; *haystack != 0; haystack++) - if (*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++) { - /* Compare with needle's remaining units. */ - const UNIT *hptr = haystack + 1; - const UNIT *nptr = needle + 1; - for (;;) + 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) { - if (*hptr != *nptr) - break; - hptr++; nptr++; - if (*nptr == 0) - return (UNIT *) haystack; + /* 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; + } } - } - return NULL; + 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 } |