match.c

/* gcc -O3 -std=c99 -o match match.c */

#include <unistd.h>


char* VALUES[] = { "false\n", "true\n" };
unsigned long SIZES[] = { 6, 5 };


int match(const char* restrict str, const char* restrict pattern) {
    const char* sBegin;
    const char* sCur;
    const char* pCur;
    char sC;
    char pC;

    for (sBegin = str; *sBegin; ++sBegin) {
        sCur = sBegin;
        pCur = pattern;
        sC = *sCur;
        pC = *pCur;
        while (sC && pC && sC == pC) {
            sC = *(++sCur);
            pC = *(++pCur);
        }

        /*
         * sC, pC
         * 0,  0  => 1  - both ran out (match)
         * 0,  x  => 0  - str ran out first => strlen(sBegin) < strlen(pattern)
         * x,  0  => 1  - pattern ran out first (match)
         * x,  y  => ?  - didn't match, but there is hope
         */
        if (!sC || !pC)
            return !pC;
    }

    /* the str was empty */
    return !*pattern;
}

/*
void test_match(char* str, char* pattern, int result) {
    int m;
    m = match(str, pattern);
    printf("match(\"%s\", \"%s\") == %s  [expected %s]\n", str, pattern, VALUES[m], VALUES[result]);
}
*/

int main(int argc, char** argv) {
    /*
    test_match("", "", 1);
    test_match("12345", "", 1);
    test_match("", "1", 0);
    test_match("12345", "123", 1);
    test_match("12345", "12_", 0);
    test_match("12345", "34", 1);
    test_match("12345", "_4", 0);
    test_match("12345", "5", 1);
    */

    int result = match(argv[1], argv[2]);
    ssize_t written = write(1, VALUES[result], SIZES[result]);
    (void)written;
    return 0;
}