[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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[2725] | 15 | *
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| 16 | * Licensed under GPLv2, see file LICENSE in this source tree.
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[821] | 17 | */
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| 18 |
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| 19 | #include "libbb.h"
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| 20 |
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[2725] | 21 | uint32_t *global_crc32_table;
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| 22 |
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| 23 | uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian)
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[1765] | 24 | {
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[821] | 25 | uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320;
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| 26 | uint32_t c;
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| 27 | int i, j;
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[1765] | 28 |
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| 29 | if (!crc_table)
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| 30 | crc_table = xmalloc(256 * sizeof(uint32_t));
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| 31 |
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[821] | 32 | for (i = 0; i < 256; i++) {
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| 33 | c = endian ? (i << 24) : i;
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| 34 | for (j = 8; j; j--) {
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| 35 | if (endian)
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| 36 | c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1);
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| 37 | else
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| 38 | c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1);
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| 39 | }
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| 40 | *crc_table++ = c;
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| 41 | }
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| 42 |
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| 43 | return crc_table - 256;
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| 44 | }
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[2725] | 45 |
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| 46 | uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
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| 47 | {
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| 48 | const void *end = (uint8_t*)buf + len;
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| 49 |
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| 50 | while (buf != end) {
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| 51 | val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf];
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| 52 | buf = (uint8_t*)buf + 1;
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| 53 | }
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| 54 | return val;
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| 55 | }
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| 56 |
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| 57 | uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table)
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| 58 | {
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| 59 | const void *end = (uint8_t*)buf + len;
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| 60 |
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| 61 | while (buf != end) {
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[3232] | 62 | val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
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[2725] | 63 | buf = (uint8_t*)buf + 1;
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| 64 | }
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| 65 | return val;
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| 66 | }
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