/**

 * Duff's Device

 * fast copy algorithm

 * performs 8 times faster on long strings.

 */

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

char *duffcopy (char *to, char *from, size_t len)

{

    size_t n, pos = 0;

    n = (len + 7) / 8;

    switch (len % 8) {

    case 0:

        do {

            to[pos] = from[pos];

            pos++;

    case 7:

            to[pos] = from[pos];

            pos++;

    case 6:

            to[pos] = from[pos];

            pos++;

    case 5:

            to[pos] = from[pos];

            pos++;

    case 4:

            to[pos] = from[pos];

            pos++;

    case 3:

            to[pos] = from[pos];

            pos++;

    case 2:

            to[pos] = from[pos];

            pos++;

    case 1:

            to[pos] = from[pos];

            pos++;

        } while (--n > 0);

    }

    return to;

}

int main (int argc, char **argv)

{

    char *to, *from;

    size_t len;

    if (argc != 2) {

        printf ("Usage: %s <string>\n", argv[0]);

        return EXIT_FAILURE;

    }

    from = argv[1];

    len = strlen (from) + 1;

    if ((to = malloc (len)) == NULL) {

        perror ("MALLOC");

        return EXIT_FAILURE;

    }

    printf ("DUFF: %s\n", duffcopy (to, from, len));

    if (to != NULL) {

        free (to);

    }

    return EXIT_SUCCESS;

}