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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9 | * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is
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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 | * Licensed under GPLv2, see file LICENSE in this source tree.
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17 | */
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18 |
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19 | #include "libbb.h"
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20 |
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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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24 | {
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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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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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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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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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62 | val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8);
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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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