96 lines
1.9 KiB
C
96 lines
1.9 KiB
C
#include "string_p.h"
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#include <string.h>
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#include <stdlib.h>
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#include <ctype.h>
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/* Quadratic-time brute-force algorithm. */
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static char *strstr_bruteforce(char const *haystack, char const *needle,
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bool ignore_case)
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{
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size_t len_needle = strlen(needle);
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while(*haystack) {
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int diff = ignore_case
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? strncasecmp(haystack, needle, len_needle)
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: strncmp(haystack, needle, len_needle);
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if(!diff) return (char *)haystack;
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haystack++;
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}
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return NULL;
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}
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/* Linear-time Knuth-Morris-Pratt algorithm. */
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static char *strstr_kmp(char const *haystack, char const *needle, int16_t *T,
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bool ignore_case)
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{
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/* Be careful, this macro has double evaluation */
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#define equal(c1, c2) \
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(ignore_case ? tolower(c1) == tolower(c2) : (c1) == (c2))
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/* Build the failure function */
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T[0] = -1;
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int cnd = 0;
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for(int pos = 1; needle[pos]; pos++, cnd++) {
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if(equal(needle[pos], needle[cnd])) {
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T[pos] = T[cnd];
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}
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else {
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T[pos] = cnd;
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while(cnd >= 0 && !equal(needle[pos], needle[cnd]))
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cnd = T[cnd];
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}
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}
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/* Perform linear-time matching */
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int i=0, pos=0;
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while(haystack[i]) {
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if(equal(needle[pos], haystack[i])) {
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pos++;
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i++;
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if(!needle[pos]) return (char *)haystack + i - pos;
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}
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else {
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pos = T[pos];
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if(pos < 0) {
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pos++;
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i++;
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}
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}
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}
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return NULL;
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}
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char *__strstr_base(char const *haystack, char const *needle,
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bool ignore_case)
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{
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size_t len_needle = strlen(needle);
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int16_t *T = NULL;
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/*
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** Don't use the KMP algorithm for huge needles (> 64 kiB) as indexes
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** might not fit in an int16_t. (In any case, if you need to search for
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** such a huge pattern, don't use strstr.)
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*/
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if(len_needle < INT16_MAX) {
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T = malloc(len_needle * sizeof *T);
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}
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/* Fall back to bruteforce if allocation fails */
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if(T) {
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char *match = strstr_kmp(haystack, needle, T, ignore_case);
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free(T);
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return match;
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}
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else {
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return strstr_bruteforce(haystack, needle, ignore_case);
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}
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}
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