diff options
author | Rob Landley <rob@landley.net> | 2006-04-10 21:07:15 +0400 |
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committer | Rob Landley <rob@landley.net> | 2006-04-10 21:07:15 +0400 |
commit | c57ec37959390ff2e43faa5e4dd5281b2923ced3 (patch) | |
tree | 8325e7bd6a9a270e931b383d33b5901751dd2a5e /libbb/crc32.c | |
parent | 998f4493756423877217239d2cc42eb8b83d50b3 (diff) |
Patch from Rob Sullivan to consolidate crc32 table generation.
Diffstat (limited to 'libbb/crc32.c')
-rw-r--r-- | libbb/crc32.c | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/libbb/crc32.c b/libbb/crc32.c new file mode 100644 index 000000000..03609952d --- /dev/null +++ b/libbb/crc32.c @@ -0,0 +1,40 @@ +/* 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 + */ + +#include <stdio.h> +#include <stdlib.h> +#include "libbb.h" + +uint32_t *bb_crc32_filltable (int endian) { + + uint32_t *crc_table = xmalloc(256 * sizeof(uint32_t)); + uint32_t polynomial = endian ? 0x04c11db7 : 0xedb88320; + uint32_t c; + int i, j; + + 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; +} |