43 lines
1.1 KiB
C
43 lines
1.1 KiB
C
/* vi: set sw=4 ts=4: */
|
|
/*
|
|
* CRC32 table fill function
|
|
* Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
|
|
* (I can't really claim much credit however, as the algorithm is
|
|
* very well-known)
|
|
*
|
|
* The following function creates a CRC32 table depending on whether
|
|
* a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
|
|
* required. Admittedly, there are other CRC32 polynomials floating
|
|
* around, but Busybox doesn't use them.
|
|
*
|
|
* endian = 1: big-endian
|
|
* endian = 0: little-endian
|
|
*
|
|
* Licensed under GPLv2, see file LICENSE in this tarball for details.
|
|
*/
|
|
|
|
#include "libbb.h"
|
|
|
|
uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
|
|
{
|
|
uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
|
|
uint32_t c;
|
|
int i, j;
|
|
|
|
if (!crc_table)
|
|
crc_table = xmalloc(256 * sizeof(uint32_t));
|
|
|
|
for (i = 0; i < 256; i++) {
|
|
c = endian ? (i << 24) : i;
|
|
for (j = 8; j; j--) {
|
|
if (endian)
|
|
c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
|
|
else
|
|
c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
|
|
}
|
|
*crc_table++ = c;
|
|
}
|
|
|
|
return crc_table - 256;
|
|
}
|