2 This file is part of GNUnet.
3 (C) 2001, 2002, 2003, 2004, 2006 Christian Grothoff (and other contributing authors)
5 GNUnet is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; either version 2, or (at your
8 option) any later version.
10 GNUnet is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with GNUnet; see the file COPYING. If not, write to the
17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 Boston, MA 02111-1307, USA.
20 For the actual CRC code:
21 Copyright abandoned; this code is in the public domain.
22 Provided to GNUnet by peter@horizon.com
26 * @file util/crypto_crc.c
27 * @brief implementation of CRC32
28 * @author Christian Grothoff
32 #include "gnunet_common.h"
33 #include "gnunet_crypto_lib.h"
35 /* Avoid wasting space on 8-byte longs. */
36 #if UINT_MAX >= 0xffffffff
37 typedef unsigned int uLong;
38 #elif ULONG_MAX >= 0xffffffff
39 typedef unsigned long uLong;
41 #error This compiler is not ANSI-compliant!
47 #define POLYNOMIAL (uLong)0xedb88320
48 static uLong crc_table[256];
51 * This routine writes each crc_table entry exactly once,
52 * with the ccorrect final value. Thus, it is safe to call
53 * even on a table that someone else is using concurrently.
66 for (i = 128; i; i >>= 1)
68 h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
69 /* h is now crc_table[i] */
70 for (j = 0; j < 256; j += 2 * i)
71 crc_table[i + j] = crc_table[j] ^ h;
76 * This computes the standard preset and inverted CRC, as used
77 * by most networking standards. Start by passing in an initial
78 * chaining value of 0, and then pass in the return value from the
79 * previous crc32() call. The final return value is the CRC.
80 * Note that this is a little-endian CRC, which is best used with
81 * data transmitted lsbit-first, and it should, itself, be appended
82 * to data in little-endian byte and bit order to preserve the
83 * property of detecting all burst errors of length 32 bits or less.
86 crc32 (uLong crc, const char *buf, size_t len)
89 GNUNET_assert (crc_table[255] != 0);
92 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
93 return crc ^ 0xffffffff;
98 * Compute the CRC32 checksum for the first len bytes of the buffer.
100 * @param buf the data over which we're taking the CRC
101 * @param len the length of the buffer
102 * @return the resulting CRC32 checksum
105 GNUNET_CRYPTO_crc32_n (const void *buf, size_t len)
109 crc = crc32 (0L, Z_NULL, 0);
110 crc = crc32 (crc, (char *) buf, len);
114 /* end of crypto_crc.c */