2 This file is part of GNUnet.
3 Copyright (C) 2001, 2002, 2003, 2004, 2006 GNUnet e.V.
5 GNUnet is free software: you can redistribute it and/or modify it
6 under the terms of the GNU Affero General Public License as published
7 by the Free Software Foundation, either version 3 of the License,
8 or (at your 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 Affero General Public License for more details.
15 You should have received a copy of the GNU Affero General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>.
18 SPDX-License-Identifier: AGPL3.0-or-later
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_crypto_lib.h"
33 #define LOG(kind, ...) GNUNET_log_from(kind, "util-crypto-crc", __VA_ARGS__)
35 /* Avoid wasting space on 8-byte longs. */
36 #if UINT_MAX >= 0xffffffff
37 typedef unsigned int GNUNET_uLong;
38 #elif ULONG_MAX >= 0xffffffff
39 typedef unsigned long GNUNET_uLong;
41 #error This compiler is not ANSI-compliant!
47 #define POLYNOMIAL (GNUNET_uLong)0xedb88320
48 static GNUNET_uLong crc_table[256];
51 * This routine writes each crc_table entry exactly once,
52 * with the correct 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(GNUNET_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);
116 * Perform an incremental step in a CRC16 (for TCP/IP) calculation.
118 * @param sum current sum, initially 0
119 * @param buf buffer to calculate CRC over (must be 16-bit aligned)
120 * @param len number of bytes in hdr, must be multiple of 2
121 * @return updated crc sum (must be subjected to #GNUNET_CRYPTO_crc16_finish() to get actual crc16)
124 GNUNET_CRYPTO_crc16_step(uint32_t sum, const void *buf, size_t len)
126 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);
171 * Calculate the checksum of a buffer in one step.
173 * @param buf buffer to calculate CRC over
174 * @param len number of bytes in @a buf
178 GNUNET_CRYPTO_crc8_n(const void *buf,
181 const uint8_t *data = buf;
182 unsigned int crc = 0;
186 for (j = len; 0 != j; j--)
188 crc ^= (*data++ << 8);
189 for (i = 8; 0 != i; i--)
191 if (0 != (crc & 0x8000))
192 crc ^= (0x1070 << 3);
196 return (uint8_t)(crc >> 8);
200 /* end of crypto_crc.c */