strstr.c

/* public domain rewrite of strstr(3) */
 
#include "ruby/missing.h"
 
size_t strlen(const char*);
 
char *
strstr(const char *haystack, const char *needle)
{
    const char *hend;
    const char *a, *b;
 
    if (*needle == 0) return (char *)haystack;
    hend = haystack + strlen(haystack) - strlen(needle) + 1;
    while (haystack < hend) {
        if (*haystack == *needle) {
            a = haystack;
            b = needle;
            for (;;) {
                if (*b == 0) return (char *)haystack;
                if (*a++ != *b++) {
                    break;
                }
            }
        }
        haystack++;
    }
    return 0;
}