/* vi: set sw=4 ts=4: */ /* * CRC32 table fill function * Copyright (C) 2006 by Rob Sullivan <cogito.ergo.cogito@gmail.com> * (I can't really claim much credit however, as the algorithm is * very well-known) * * The following function creates a CRC32 table depending on whether * a big-endian (0x04c11db7) or little-endian (0xedb88320) CRC32 is * required. Admittedly, there are other CRC32 polynomials floating * around, but Busybox doesn't use them. * * endian = 1: big-endian * endian = 0: little-endian * * Licensed under GPLv2, see file LICENSE in this source tree. */ #include "libbb.h" uint32_t *global_crc32_table; uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian) { uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; uint32_t c; unsigned i, j; if (!crc_table) crc_table = xmalloc(256 * sizeof(uint32_t)); for (i = 0; i < 256; i++) { c = endian ? (i << 24) : i; for (j = 8; j; j--) { if (endian) c = (c&0x80000000) ? ((c << 1) ^ polynomial) : (c << 1); else c = (c&1) ? ((c >> 1) ^ polynomial) : (c >> 1); } *crc_table++ = c; } return crc_table - 256; } uint32_t FAST_FUNC crc32_block_endian1(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) { const void *end = (uint8_t*)buf + len; while (buf != end) { val = (val << 8) ^ crc_table[(val >> 24) ^ *(uint8_t*)buf]; buf = (uint8_t*)buf + 1; } return val; } uint32_t FAST_FUNC crc32_block_endian0(uint32_t val, const void *buf, unsigned len, uint32_t *crc_table) { const void *end = (uint8_t*)buf + len; while (buf != end) { val = crc_table[(uint8_t)val ^ *(uint8_t*)buf] ^ (val >> 8); buf = (uint8_t*)buf + 1; } return val; }