duff.c
author Markus Bröker<broeker.markus@googlemail.com>
Sun, 10 Feb 2019 13:17:01 +0100
changeset 173 374a86886bc5
parent 63 5a82f89d607e
permissions -rw-r--r--
LAST-DIGIT-BUG: INCREMENT before LF
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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/**
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 * Duff's Device
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 * fast copy algorithm
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 * performs 8 times faster on long strings.
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 */
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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char *duffcopy (char *to, char *from, size_t len)
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{
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    size_t n, pos = 0;
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    n = (len + 7) / 8;
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    switch (len % 8) {
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    case 0:
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        do {
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            to[pos] = from[pos];
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            pos++;
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    case 7:
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            to[pos] = from[pos];
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            pos++;
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    case 6:
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            to[pos] = from[pos];
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            pos++;
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    case 5:
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            to[pos] = from[pos];
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            pos++;
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    case 4:
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            to[pos] = from[pos];
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            pos++;
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    case 3:
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            to[pos] = from[pos];
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            pos++;
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    case 2:
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            to[pos] = from[pos];
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            pos++;
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    case 1:
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            to[pos] = from[pos];
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            pos++;
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        } while (--n > 0);
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    }
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    return to;
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}
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int main (int argc, char **argv)
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{
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    char *to, *from;
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    size_t len;
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    if (argc != 2) {
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        printf ("Usage: %s <string>\n", argv[0]);
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        return EXIT_FAILURE;
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    }
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    from = argv[1];
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    len = strlen (from) + 1;
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    if ((to = malloc (len)) == NULL) {
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        perror ("MALLOC");
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        return EXIT_FAILURE;
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    }
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    printf ("DUFF: %s\n", duffcopy (to, from, len));
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    if (to != NULL) {
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        free (to);
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    }
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    return EXIT_SUCCESS;
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}