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 17#include "libbb.h" 18 19uint32_t *crc32_filltable(uint32_t *crc_table, int endian) 20{ 21 uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; 22 uint32_t c; 23 int i, j; 24 25 if (!crc_table) 26 crc_table = xmalloc(256 * sizeof(uint32_t)); 27 28 for (i = 0; i < 256; i++) { 29 c = endian ? (i << 24) : i; 30 for (j = 8; j; j--) { 31 if (endian) 32 c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1); 33 else 34 c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1); 35 } 36 *crc_table++ = c; 37 } 38 39 return crc_table - 256; 40} 41