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