gistfile1.c

/* Author  : Ross Williams (ross@guest.adelaide.edu.au.).                     */
/* Date    : 3 June 1993.                                                     */
/* Version : 1.0.                                                             */
/* Status  : Public domain.                                                   */

/* statically configured to produce any table covered by the Rocksoft^tm      */
/* Model CRC Algorithm. For more information on the Rocksoft^tm Model CRC     */
/* Algorithm, see the document titled "A Painless Guide to CRC Error          */
/* Detection Algorithms" by Ross Williams (ross@guest.adelaide.edu.au.). This */
/* document is likely to be in "ftp.adelaide.edu.au/pub/rocksoft".            */
/*                                                                            */
/* Note: Rocksoft is a trademark of Rocksoft Pty Ltd, Adelaide, Australia.    */

#include <stdio.h>
#include <stdlib.h>

#define TB_BITS   32
#define TB_POLY   0x1EDC6F41L
#define TB_TOPBIT 1L << (TB_BITS-1)

static void gentable(uint32_t *table);
static uint32_t cm_tab(int index);
static uint32_t reflect(uint32_t v, int b);

int
main(int argc, char *argv[])
{
    uint32_t iscsiCrc32Table1[256];
    uint32_t *table = &iscsiCrc32Table1[0];

    gentable(table);
}

static void
gentable(uint32_t *table)
{
    int i;

    for (i = 0; i < 256; ++i) {
        table[i] = cm_tab(i);
    }
}

static uint32_t
cm_tab(int index)
{
    int   i;
    uint32_t r;
    uint32_t inbyte = (ulong)index;

    inbyte = reflect(inbyte, 8);
    r = inbyte << (TB_BITS-8);
    for (i = 0; i < 8; ++i) {
        if (r & TB_TOPBIT)
            r = (r << 1) ^ TB_POLY;
        else
            r <<= 1;
    }
    r = reflect(r, TB_BITS);

    return (r);
}

/*
 * Returns the value v with the bottom b [0,32] bits reflected.
 * Example: reflect(0x3e23L,3) == 0x3e26
 */
static uint32_t
reflect(uint32_t v, int b)
{
    int i;
    uint32_t t = v;

    for (i=0; i<b; i++) {
        if (t & 1L)
            v |=  1L << ((b-1) - i);
        else
            v &= ~(1L << ((b-1) - i));

        t >>= 1;
    }

    return (v);
}