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Diffstat (limited to 'src/util/crypto_crc.c')
| -rw-r--r-- | src/util/crypto_crc.c | 171 |
1 files changed, 171 insertions, 0 deletions
diff --git a/src/util/crypto_crc.c b/src/util/crypto_crc.c new file mode 100644 index 0000000..8bccf6b --- /dev/null +++ b/src/util/crypto_crc.c @@ -0,0 +1,171 @@ +/* + This file is part of GNUnet. + (C) 2001, 2002, 2003, 2004, 2006 Christian Grothoff (and other contributing authors) + + GNUnet is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published + by the Free Software Foundation; either version 2, or (at your + option) any later version. + + GNUnet is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. + + You should have received a copy of the GNU General Public License + along with GNUnet; see the file COPYING. If not, write to the + Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. + + For the actual CRC-32 code: + Copyright abandoned; this code is in the public domain. + Provided to GNUnet by peter@horizon.com +*/ + +/** + * @file util/crypto_crc.c + * @brief implementation of CRC16 and CRC32 + * @author Christian Grothoff + */ + +#include "platform.h" +#include "gnunet_common.h" +#include "gnunet_crypto_lib.h" + +#define LOG(kind,...) GNUNET_log_from (kind, "util", __VA_ARGS__) + +/* Avoid wasting space on 8-byte longs. */ +#if UINT_MAX >= 0xffffffff +typedef unsigned int uLong; +#elif ULONG_MAX >= 0xffffffff +typedef unsigned long uLong; +#else +#error This compiler is not ANSI-compliant! +#endif + +#define Z_NULL 0 + + +#define POLYNOMIAL (uLong)0xedb88320 +static uLong crc_table[256]; + +/* + * This routine writes each crc_table entry exactly once, + * with the ccorrect final value. Thus, it is safe to call + * even on a table that someone else is using concurrently. + */ +static void +crc_init () +{ + static int once; + unsigned int i, j; + uLong h = 1; + + if (once) + return; + once = 1; + crc_table[0] = 0; + for (i = 128; i; i >>= 1) + { + h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0); + /* h is now crc_table[i] */ + for (j = 0; j < 256; j += 2 * i) + crc_table[i + j] = crc_table[j] ^ h; + } +} + +/* + * This computes the standard preset and inverted CRC, as used + * by most networking standards. Start by passing in an initial + * chaining value of 0, and then pass in the return value from the + * previous crc32() call. The final return value is the CRC. + * Note that this is a little-endian CRC, which is best used with + * data transmitted lsbit-first, and it should, itself, be appended + * to data in little-endian byte and bit order to preserve the + * property of detecting all burst errors of length 32 bits or less. + */ +static uLong +crc32 (uLong crc, const char *buf, size_t len) +{ + crc_init (); + GNUNET_assert (crc_table[255] != 0); + crc ^= 0xffffffff; + while (len--) + crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff]; + return crc ^ 0xffffffff; +} + + +/** + * Compute the CRC32 checksum for the first len bytes of the buffer. + * + * @param buf the data over which we're taking the CRC + * @param len the length of the buffer + * @return the resulting CRC32 checksum + */ +int32_t +GNUNET_CRYPTO_crc32_n (const void *buf, size_t len) +{ + uLong crc; + + crc = crc32 (0L, Z_NULL, 0); + crc = crc32 (crc, (char *) buf, len); + return crc; +} + + +/** + * Perform an incremental step in a CRC16 (for TCP/IP) calculation. + * + * @param sum current sum, initially 0 + * @param buf buffer to calculate CRC over (must be 16-bit aligned) + * @param len number of bytes in hdr, must be multiple of 2 + * @return updated crc sum (must be subjected to GNUNET_CRYPTO_crc16_finish to get actual crc16) + */ +uint32_t +GNUNET_CRYPTO_crc16_step (uint32_t sum, const void *buf, size_t len) +{ + const uint16_t *hdr = buf; + for (; len >= 2; len -= 2) + sum += *(hdr++); + if (len == 1) + sum += (*hdr) & ntohs(0xFF00); + return sum; +} + + +/** + * Convert results from GNUNET_CRYPTO_crc16_step to final crc16. + * + * @param sum cummulative sum + * @return crc16 value + */ +uint16_t +GNUNET_CRYPTO_crc16_finish (uint32_t sum) +{ + sum = (sum >> 16) + (sum & 0xFFFF); + sum += (sum >> 16); + + return ~sum; +} + + +/** + * Calculate the checksum of a buffer in one step. + * + * @param buf buffer to calculate CRC over (must be 16-bit aligned) + * @param len number of bytes in hdr, must be multiple of 2 + * @return crc16 value + */ +uint16_t +GNUNET_CRYPTO_crc16_n (const void *buf, size_t len) +{ + const uint16_t *hdr = buf; + uint32_t sum = GNUNET_CRYPTO_crc16_step (0, hdr, len); + + return GNUNET_CRYPTO_crc16_finish (sum); +} + + + +/* end of crypto_crc.c */ |