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41 lines
1.0 KiB
C
41 lines
1.0 KiB
C
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/* vi: set sw=4 ts=4: */
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/*
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* CRC32 table fill function
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* Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
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* (I can't really claim much credit however, as the algorithm is
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* very well-known)
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*
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* The following function creates a CRC32 table depending on whether
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* a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
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* required. Admittedly, there are other CRC32 polynomials floating
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* around, but Busybox doesn't use them.
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*
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* endian = 1: big-endian
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* endian = 0: little-endian
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "libbb.h"
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uint32_t *bb_crc32_filltable (int endian) {
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uint32_t *crc_table = xmalloc(256 * sizeof(uint32_t));
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uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
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uint32_t c;
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int i, j;
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for (i = 0; i < 256; i++) {
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c = endian ? (i << 24) : i;
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for (j = 8; j; j--) {
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if (endian)
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c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
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else
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c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
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}
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*crc_table++ = c;
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}
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return crc_table - 256;
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}
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