mirror of
https://github.com/cryb-to/cryb-to.git
synced 2024-12-20 19:41:08 +00:00
72 lines
2.6 KiB
C
72 lines
2.6 KiB
C
/*-
|
||
* Copyright (c) 2015 Dag-Erling Smørgrav
|
||
* All rights reserved.
|
||
*
|
||
* Redistribution and use in source and binary forms, with or without
|
||
* modification, are permitted provided that the following conditions
|
||
* are met:
|
||
* 1. Redistributions of source code must retain the above copyright
|
||
* notice, this list of conditions and the following disclaimer.
|
||
* 2. Redistributions in binary form must reproduce the above copyright
|
||
* notice, this list of conditions and the following disclaimer in the
|
||
* documentation and/or other materials provided with the distribution.
|
||
* 3. The name of the author may not be used to endorse or promote
|
||
* products derived from this software without specific prior written
|
||
* permission.
|
||
*
|
||
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
||
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
||
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
||
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
||
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
||
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
||
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
||
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
||
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
||
* SUCH DAMAGE.
|
||
*/
|
||
|
||
#include "cryb/impl.h"
|
||
|
||
#include <stdint.h>
|
||
#include <string.h>
|
||
|
||
#include <cryb/bitwise.h>
|
||
#include <cryb/endian.h>
|
||
#include <cryb/hash.h>
|
||
|
||
/*
|
||
* Simple implementation of the 64-bit variant of Fletcher's checksum,
|
||
* described in Fletcher, J. G. (January 1982), "An Arithmetic Checksum
|
||
* for Serial Transmissions", IEEE Transactions on Communications. COM-30
|
||
* (1): 247–252, doi:10.1109/tcom.1982.1095369
|
||
*
|
||
* The paper assumes that the input length is a multiple of the checksum
|
||
* algorithm's word size (half the checksum size). This implementation
|
||
* will zero-pad the input up to the nearest multiple of the word size.
|
||
*/
|
||
uint64_t
|
||
fletcher64_hash(const void *data, size_t len)
|
||
{
|
||
const uint8_t *bytes;
|
||
uint64_t c0, c1;
|
||
uint32_t w;
|
||
|
||
for (bytes = data, c0 = c1 = 0; len > 3; len -= 4, bytes += 4) {
|
||
/* replace with be32toh() if input is aligned */
|
||
w = be32dec(bytes);
|
||
c0 = (c0 + w) % 0xffffffffU;
|
||
c1 = (c1 + c0) % 0xffffffffU;
|
||
}
|
||
if (len > 0) {
|
||
w = bytes[0] << 24;
|
||
if (len > 1)
|
||
w |= bytes[1] << 16;
|
||
if (len > 2)
|
||
w |= bytes[2] << 8;
|
||
c0 = (c0 + w) % 0xffffffffU;
|
||
c1 = (c1 + c0) % 0xffffffffU;
|
||
}
|
||
return (c1 << 32 | c0);
|
||
}
|