| /* 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 tarball for details. |
| */ |
| |
| #include "libbb.h" |
| |
| uint32_t* FAST_FUNC crc32_filltable(uint32_t *crc_table, int endian) |
| { |
| uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; |
| uint32_t c; |
| int 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; |
| } |