1/* vi: set sw=4 ts=4: */ 2/* 3 * CRC32 table fill function 4 * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com> 5 * (I can't really claim much credit however, as the algorithm is 6 * very well-known) 7 * 8 * The following function creates a CRC32 table depending on whether 9 * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is 10 * required. Admittedly, there are other CRC32 polynomials floating 11 * around, but Busybox doesn't use them. 12 * 13 * endian = 1: big-endian 14 * endian = 0: little-endian 15 * 16 * Licensed under GPLv2, see file LICENSE in this source tree. 17 */ 18#include "libbb.h" 19 20uint32_t *global_crc32_table; 21 22uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian) 23{ 24 uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; 25 uint32_t c; 26 unsigned i, j; 27 28 if (!crc_table) 29 crc_table = xmalloc(256 * sizeof(uint32_t)); 30 31 for (i = 0; i < 256; i++) { 32 c = endian ? (i << 24) : i; 33 for (j = 8; j; j--) { 34 if (endian) 35 c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1); 36 else 37 c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1); 38 } 39 *crc_table++ = c; 40 } 41 42 return crc_table - 256; 43} 44/* Common uses: */ 45uint32_t* FAST_FUNC crc32_new_table_le(void) 46{ 47 return crc32_filltable(NULL, 0); 48} 49uint32_t* FAST_FUNC global_crc32_new_table_le(void) 50{ 51 global_crc32_table = crc32_new_table_le(); 52 return global_crc32_table; 53} 54 55uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) 56{ 57 const void *end = (uint8_t*)buf + len; 58 59 while (buf != end) { 60 val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf]; 61 buf = (uint8_t*)buf + 1; 62 } 63 return val; 64} 65 66uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) 67{ 68 const void *end = (uint8_t*)buf + len; 69 70 while (buf != end) { 71 val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8); 72 buf = (uint8_t*)buf + 1; 73 } 74 return val; 75} 76