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[821] | 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * CRC32 table fill function
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| 4 | * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
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| 5 | * (I can't really claim much credit however, as the algorithm is
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| 6 | * very well-known)
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| 7 | *
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| 8 | * The following function creates a CRC32 table depending on whether
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[1765] | 9 | * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
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[821] | 10 | * required. Admittedly, there are other CRC32 polynomials floating
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| 11 | * around, but Busybox doesn't use them.
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| 12 | *
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| 13 | * endian = 1: big-endian
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| 14 | * endian = 0: little-endian
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| 15 | */
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| 16 |
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| 17 | #include "libbb.h"
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| 18 |
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[1765] | 19 | uint32_t *crc32_filltable(uint32_t *crc_table, int endian)
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| 20 | {
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[821] | 21 | uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
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| 22 | uint32_t c;
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| 23 | int i, j;
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[1765] | 24 |
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| 25 | if (!crc_table)
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| 26 | crc_table = xmalloc(256 * sizeof(uint32_t));
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| 27 |
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[821] | 28 | for (i = 0; i < 256; i++) {
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| 29 | c = endian ? (i << 24) : i;
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| 30 | for (j = 8; j; j--) {
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| 31 | if (endian)
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| 32 | c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
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| 33 | else
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| 34 | c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
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| 35 | }
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| 36 | *crc_table++ = c;
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| 37 | }
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| 38 |
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| 39 | return crc_table - 256;
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| 40 | }
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