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 3, 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
31 #include "gnunet_common.h"
32 #include "gnunet_crypto_lib.h"
34 #define LOG(kind,...) GNUNET_log_from (kind, "util", __VA_ARGS__)
36 /* Avoid wasting space on 8-byte longs. */
37 #if UINT_MAX >= 0xffffffff
38 typedef unsigned int uLong;
39 #elif ULONG_MAX >= 0xffffffff
40 typedef unsigned long uLong;
42 #error This compiler is not ANSI-compliant!
48 #define POLYNOMIAL (uLong)0xedb88320
49 static uLong crc_table[256];
52 * This routine writes each crc_table entry exactly once,
53 * with the correct final value. Thus, it is safe to call
54 * even on a table that someone else is using concurrently.
67 for (i = 128; i; i >>= 1)
69 h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
70 /* h is now crc_table[i] */
71 for (j = 0; j < 256; j += 2 * i)
72 crc_table[i + j] = crc_table[j] ^ h;
77 * This computes the standard preset and inverted CRC, as used
78 * by most networking standards. Start by passing in an initial
79 * chaining value of 0, and then pass in the return value from the
80 * previous crc32() call. The final return value is the CRC.
81 * Note that this is a little-endian CRC, which is best used with
82 * data transmitted lsbit-first, and it should, itself, be appended
83 * to data in little-endian byte and bit order to preserve the
84 * property of detecting all burst errors of length 32 bits or less.
87 crc32 (uLong crc, const char *buf, size_t len)
90 GNUNET_assert (crc_table[255] != 0);
93 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
94 return crc ^ 0xffffffff;
99 * Compute the CRC32 checksum for the first len bytes of the buffer.
101 * @param buf the data over which we're taking the CRC
102 * @param len the length of the buffer
103 * @return the resulting CRC32 checksum
106 GNUNET_CRYPTO_crc32_n (const void *buf, size_t len)
110 crc = crc32 (0L, Z_NULL, 0);
111 crc = crc32 (crc, (char *) buf, len);
117 * Perform an incremental step in a CRC16 (for TCP/IP) calculation.
119 * @param sum current sum, initially 0
120 * @param buf buffer to calculate CRC over (must be 16-bit aligned)
121 * @param len number of bytes in hdr, must be multiple of 2
122 * @return updated crc sum (must be subjected to GNUNET_CRYPTO_crc16_finish to get actual crc16)
125 GNUNET_CRYPTO_crc16_step (uint32_t sum, const void *buf, size_t len)
127 const uint16_t *hdr = buf;
128 for (; len >= 2; len -= 2)
131 sum += (*hdr) & ntohs(0xFF00);
137 * Convert results from GNUNET_CRYPTO_crc16_step to final crc16.
139 * @param sum cummulative sum
140 * @return crc16 value
143 GNUNET_CRYPTO_crc16_finish (uint32_t sum)
145 sum = (sum >> 16) + (sum & 0xFFFF);
153 * Calculate the checksum of a buffer in one step.
155 * @param buf buffer to calculate CRC over (must be 16-bit aligned)
156 * @param len number of bytes in hdr, must be multiple of 2
157 * @return crc16 value
160 GNUNET_CRYPTO_crc16_n (const void *buf, size_t len)
162 const uint16_t *hdr = buf;
163 uint32_t sum = GNUNET_CRYPTO_crc16_step (0, hdr, len);
165 return GNUNET_CRYPTO_crc16_finish (sum);
170 /* end of crypto_crc.c */