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/*
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 correct 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 */
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