/*
 * costs.c -- calculate costs of strncmp against memmove
 *
 * Dmitri Tikhonov
 * February 8, 2006
 */

#include <sys/time.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

#define STRLEN 40
#define MEMLEN (1 << 10)

static void
usage (const char *progname)
{
    fprintf(stderr, "Usage: %s repetitions\n", progname);
    return;
}


int
main (int argc, char **argv)
{
    int i, n, fd, diff;
    struct timeval t[2];
    struct timezone dummy;  /* not used */
    char a[STRLEN], b[STRLEN];
    char *data;

    if (argc < 2) {
        usage(*argv);
        exit(1);
    }

    n = atoi(argv[1]);

    if (n < 0) {
        fprintf(stderr, "argument should be a positive integer\n");
        exit(2);
    }

    /* Get two random strings from /dev/random */
    if (-1 == (fd = open("/dev/random", O_RDONLY))) {
        perror("Cannot open /dev/random");
        exit(3);
    }
    read(fd, a, STRLEN);
    read(fd, b, STRLEN);
    close(fd);

    gettimeofday(&t[0], &dummy);

    for (i = 0; i < n; ++i)
        strncmp(a, b, STRLEN);

    gettimeofday(&t[1], &dummy);

    diff = 1000000 * (t[1].tv_sec - t[0].tv_sec) +
           (t[1].tv_usec - t[0].tv_usec);

    printf("Average cost of strncmp: %.2f nanoseconds\n",
            (float) 1000 * diff / n);

    data = malloc(MEMLEN + 1);

    gettimeofday(&t[0], &dummy);

    for (i = 0; i < n; ++i)
        memmove(data + 1, data, MEMLEN);

    gettimeofday(&t[1], &dummy);

    diff = 1000000 * (t[1].tv_sec - t[0].tv_sec) +
           (t[1].tv_usec - t[0].tv_usec);

    printf("Average cost of memmove: %.2f nanoseconds\n",
            (float) 1000 * diff / n);
    exit(0);
}