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40 lines
953 B
40 lines
953 B
/* |
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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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