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-32 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 CRC16 and CRC32
28 * @author Christian Grothoff
32 #include "gnunet_common.h"
33 #include "gnunet_crypto_lib.h"
35 #define LOG(kind,...) GNUNET_log_from (kind, "util", __VA_ARGS__)
37 /* Avoid wasting space on 8-byte longs. */
38 #if UINT_MAX >= 0xffffffff
39 typedef unsigned int uLong;
40 #elif ULONG_MAX >= 0xffffffff
41 typedef unsigned long uLong;
43 #error This compiler is not ANSI-compliant!
49 #define POLYNOMIAL (uLong)0xedb88320
50 static uLong crc_table[256];
53 * This routine writes each crc_table entry exactly once,
54 * with the ccorrect final value. Thus, it is safe to call
55 * even on a table that someone else is using concurrently.
68 for (i = 128; i; i >>= 1)
70 h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
71 /* h is now crc_table[i] */
72 for (j = 0; j < 256; j += 2 * i)
73 crc_table[i + j] = crc_table[j] ^ h;
78 * This computes the standard preset and inverted CRC, as used
79 * by most networking standards. Start by passing in an initial
80 * chaining value of 0, and then pass in the return value from the
81 * previous crc32() call. The final return value is the CRC.
82 * Note that this is a little-endian CRC, which is best used with
83 * data transmitted lsbit-first, and it should, itself, be appended
84 * to data in little-endian byte and bit order to preserve the
85 * property of detecting all burst errors of length 32 bits or less.
88 crc32 (uLong crc, const char *buf, size_t len)
91 GNUNET_assert (crc_table[255] != 0);
94 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
95 return crc ^ 0xffffffff;
100 * Compute the CRC32 checksum for the first len bytes of the buffer.
102 * @param buf the data over which we're taking the CRC
103 * @param len the length of the buffer
104 * @return the resulting CRC32 checksum
107 GNUNET_CRYPTO_crc32_n (const void *buf, size_t len)
111 crc = crc32 (0L, Z_NULL, 0);
112 crc = crc32 (crc, (char *) buf, len);
118 * Perform an incremental step in a CRC16 (for TCP/IP) calculation.
120 * @param sum current sum, initially 0
121 * @param buf buffer to calculate CRC over (must be 16-bit aligned)
122 * @param len number of bytes in hdr, must be multiple of 2
123 * @return updated crc sum (must be subjected to GNUNET_CRYPTO_crc16_finish to get actual crc16)
126 GNUNET_CRYPTO_crc16_step (uint32_t sum, const void *buf, size_t len)
128 const uint16_t *hdr = buf;
129 for (; len >= 2; len -= 2)
132 sum += (*hdr) & ntohs(0xFF00);
138 * Convert results from GNUNET_CRYPTO_crc16_step to final crc16.
140 * @param sum cummulative sum
141 * @return crc16 value
144 GNUNET_CRYPTO_crc16_finish (uint32_t sum)
146 sum = (sum >> 16) + (sum & 0xFFFF);
154 * Calculate the checksum of a buffer in one step.
156 * @param buf buffer to calculate CRC over (must be 16-bit aligned)
157 * @param len number of bytes in hdr, must be multiple of 2
158 * @return crc16 value
161 GNUNET_CRYPTO_crc16_n (const void *buf, size_t len)
163 const uint16_t *hdr = buf;
164 uint32_t sum = GNUNET_CRYPTO_crc16_step (0, hdr, len);
166 return GNUNET_CRYPTO_crc16_finish (sum);
171 /* end of crypto_crc.c */