91 lines
2.4 KiB
C
91 lines
2.4 KiB
C
#include <string.h>
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#include <stdlib.h>
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#include <stddef.h>
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#if (__STDC_VERSION__ >= 199901L)
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#include <stdint.h>
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#endif
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char *repl_str(const char *str, const char *from, const char *to) {
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/* Adjust each of the below values to suit your needs. */
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/* Increment positions cache size initially by this number. */
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size_t cache_sz_inc = 16;
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/* Thereafter, each time capacity needs to be increased,
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* multiply the increment by this factor. */
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const size_t cache_sz_inc_factor = 3;
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/* But never increment capacity by more than this number. */
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const size_t cache_sz_inc_max = 1048576;
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char *pret, *ret = NULL;
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const char *pstr2, *pstr = str;
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size_t i, count = 0;
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#if (__STDC_VERSION__ >= 199901L)
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uintptr_t *pos_cache_tmp, *pos_cache = NULL;
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#else
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ptrdiff_t *pos_cache_tmp, *pos_cache = NULL;
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#endif
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size_t cache_sz = 0;
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size_t cpylen, orglen, retlen, tolen, fromlen = strlen(from);
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/* Find all matches and cache their positions. */
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while ((pstr2 = strstr(pstr, from)) != NULL) {
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count++;
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/* Increase the cache size when necessary. */
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if (cache_sz < count) {
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cache_sz += cache_sz_inc;
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pos_cache_tmp = realloc(pos_cache, sizeof(*pos_cache) * cache_sz);
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if (pos_cache_tmp == NULL) {
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goto end_repl_str;
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} else pos_cache = pos_cache_tmp;
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cache_sz_inc *= cache_sz_inc_factor;
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if (cache_sz_inc > cache_sz_inc_max) {
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cache_sz_inc = cache_sz_inc_max;
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}
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}
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pos_cache[count-1] = pstr2 - str;
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pstr = pstr2 + fromlen;
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}
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orglen = pstr - str + strlen(pstr);
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/* Allocate memory for the post-replacement string. */
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if (count > 0) {
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tolen = strlen(to);
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retlen = orglen + (tolen - fromlen) * count;
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} else retlen = orglen;
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ret = malloc(retlen + 1);
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if (ret == NULL) {
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goto end_repl_str;
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}
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if (count == 0) {
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/* If no matches, then just duplicate the string. */
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strcpy(ret, str);
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} else {
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/* Otherwise, duplicate the string whilst performing
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* the replacements using the position cache. */
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pret = ret;
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memcpy(pret, str, pos_cache[0]);
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pret += pos_cache[0];
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for (i = 0; i < count; i++) {
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memcpy(pret, to, tolen);
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pret += tolen;
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pstr = str + pos_cache[i] + fromlen;
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cpylen = (i == count-1 ? orglen : pos_cache[i+1]) - pos_cache[i] - fromlen;
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memcpy(pret, pstr, cpylen);
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pret += cpylen;
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}
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ret[retlen] = '\0';
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}
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end_repl_str:
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/* Free the cache and return the post-replacement string,
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* which will be NULL in the event of an error. */
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free(pos_cache);
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return ret;
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}
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