Optimizing strong compare

strcmp.c

/* Time-stamp: <2013-07-07 10:37:24 dky> */

#include <stdio.h>
#include <string.h>

int stringcompare(const char*, const char*);
int stringcompareopt(const char *, size_t, const char *, size_t);

int stringcompare(const char *s1, const char *s2) {
    size_t idx = 0;
    int ret = 0;

    if (s1 == s2) {
    return 0;
    } else if (NULL == s2) {
	return 1;
    } else if (NULL == s1) {
	return -1;
    }

    /* Consider loop unrolling if string lenghts are known */
    for (idx = 0; s1[idx] && s2[idx]; ++idx) {
	if (s1[idx] < s2[idx]) {
	    ret = -1;
	    break;
	} else if (s1[idx] > s2[idx]) {
	    ret = 1;
	    break;
	}
    }

    if (0 == ret) {
	/* Check if there is still data in the strings */
	if (s1[idx]) {
	    ret = 1;
	} else if (s2[idx]) {
	    ret = -1;
	}
    }

    return ret;
}

int stringcompareopt(const char *s1, size_t l1, const char *s2, size_t l2) {
    if (s1 == s2) {
	return 0;
    } else if (0 == l1 && 0 == l2) {
	return 0;
    } else if (NULL == s2) {
	return 1;
    } else if (NULL == s1) {
	return -1;
    }

    /* Both strings are non zero length and have the same length */
    size_t idx = 0;
    size_t min = (l1 < l2) ? l1 : l2;
    while (min - idx) {
	if (sizeof(size_t) > (min - idx)) {
	    if (s1[idx] < s2[idx]) {
		return -1;
	    } else if (s1[idx] > s2[idx]) {
		return 1;
	    }
	    ++idx;
	} else {		/* Loop unrolling */
	    size_t *u1 = (size_t *)(s1 + idx),
		*u2 = (size_t *)(s2 + idx);
	    if (*u1 < *u2) {
		return -1;
	    } else if (*u1 > *u2) {
		return 1;
	    }
	    idx += sizeof(size_t);
	}
    }

    int ret = l1 - l2;
    if (ret < 0) {
	ret  = -1;
    } else if (ret > 0) {
	ret = 1;
    }

    return ret;
}

int main(int argc, char *argv[]) {
    if (argc < 3) {
	fprintf(stderr, "Usage: %s string1 string2\n", argv[0]);
	return -1;
    }

    /* Use the library function to check for correctness */
    printf("Comparing using strcmp: %d\n", strcmp(argv[1], argv[2]));

    /* Byte-wise comparison */
    printf("Comparing using stringcompare: %d\n", stringcompare(argv[1],
								argv[2]));

    /* If the string length is known: Unroll the loop */
    printf("Comparing using stringcompareopt: %d\n",
	   stringcompareopt(argv[1], strlen(argv[1]),
			    argv[2], strlen(argv[2])));

    return 0;
}