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/* 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
*/
#include <stdio.h>
#include <stdlib.h>
#include "libbb.h"
uint32_t *bb_crc32_filltable (int endian) {
uint32_t *crc_table = xmalloc(256 * sizeof(uint32_t));
uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
uint32_t c;
int i, j;
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;
}
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