2015-08-17 15:21:47 +00:00
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/*-
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* Copyright (c) 2015 Dag-Erling Smørgrav
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "cryb/impl.h"
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#include <stdint.h>
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#include <string.h>
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#include <cryb/bitwise.h>
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#include <cryb/endian.h>
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#include <cryb/hash.h>
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/*
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2015-08-18 10:42:41 +00:00
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* Simple implementation of the 32-bit variant of Fletcher's checksum,
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* described in Fletcher, J. G. (January 1982), "An Arithmetic Checksum
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* for Serial Transmissions", IEEE Transactions on Communications. COM-30
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* (1): 247–252, doi:10.1109/tcom.1982.1095369
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*
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* The paper assumes that the input length is a multiple of the checksum
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* algorithm's word size (half the checksum size). This implementation
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* will zero-pad the input up to the nearest multiple of the word size.
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2015-08-17 15:21:47 +00:00
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*/
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uint32_t
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fletcher32_hash(const void *data, size_t len)
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{
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const uint8_t *bytes;
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uint32_t c0, c1;
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uint16_t w;
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for (bytes = data, c0 = c1 = 0; len > 1; len -= 2, bytes += 2) {
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/* replace with be16toh() if input is aligned */
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w = be16dec(bytes);
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c0 = (c0 + w) % 0xffffU;
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c1 = (c1 + c0) % 0xffffU;
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}
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if (len > 0) {
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w = bytes[0] << 8;
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c0 = (c0 + w) % 0xffffffffU;
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c1 = (c1 + c0) % 0xffffffffU;
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}
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return (c1 << 16 | c0);
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}
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