1 /**

     2  * Duff's Device

     3  * fast copy algorithm

     4  * performs 8 times faster on long strings.

     5  */

     6 

     7 #include <stdio.h>

     8 #include <stdlib.h>

     9 #include <string.h>

    10 

    11 char *duffcopy (char *to, char *from, int num)

    12 {

    13     int n, pos = 0;

    14 

    15     n = (num + 7) / 8;

    16 

    17     switch (num % 8) {

    18     case 0:

    19         do {

    20             to[pos] = from[pos];

    21             pos++;

    22     case 7:

    23             to[pos] = from[pos];

    24             pos++;

    25     case 6:

    26             to[pos] = from[pos];

    27             pos++;

    28     case 5:

    29             to[pos] = from[pos];

    30             pos++;

    31     case 4:

    32             to[pos] = from[pos];

    33             pos++;

    34     case 3:

    35             to[pos] = from[pos];

    36             pos++;

    37     case 2:

    38             to[pos] = from[pos];

    39             pos++;

    40     case 1:

    41             to[pos] = from[pos];

    42             pos++;

    43         } while (--n > 0);

    44     }

    45 

    46     return to;

    47 }

    48 

    49 int main (int argc, char **argv)

    50 {

    51     char to[80], *from;

    52 

    53     if (argc != 2) {

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

    55         return EXIT_FAILURE;

    56     }

    57 

    58     from = argv[1];

    59 

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

    61     return EXIT_SUCCESS;

    62 }