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41 lines
953 B
C
41 lines
953 B
C
/*
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* Copyright 2015 Eistec AB
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*
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* This file is subject to the terms and conditions of the GNU Lesser
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* General Public License v2.1. See the file LICENSE in the top level
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* directory for more details.
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*/
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/**
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* @ingroup sys_checksum_fletcher16
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* @{
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*
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* @file
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* @brief Fletcher16 implementation
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*
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* @author Joakim Nohlgård <joakim.nohlgard@eistec.se>
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*
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* @}
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*/
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#include "checksum/fletcher16.h"
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uint16_t fletcher16(const uint8_t *data, size_t bytes)
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{
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uint16_t sum1 = 0xff, sum2 = 0xff;
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while (bytes) {
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size_t tlen = bytes > 20 ? 20 : bytes;
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bytes -= tlen;
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do {
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sum2 += sum1 += *data++;
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} while (--tlen);
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sum1 = (sum1 & 0xff) + (sum1 >> 8);
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sum2 = (sum2 & 0xff) + (sum2 >> 8);
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}
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/* Second reduction step to reduce sums to 8 bits */
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sum1 = (sum1 & 0xff) + (sum1 >> 8);
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sum2 = (sum2 & 0xff) + (sum2 >> 8);
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return (sum2 << 8) | sum1;
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}
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