mirror of
https://github.com/RIOT-OS/RIOT.git
synced 2024-12-29 04:50:03 +01:00
Koen Zandberg
230c5b89de
This commit extends the fletcher16 function with a set of init, update and finish functions to allow for multi-part checksums. This is useful when the data that has to be checksummed is not available in a single continuous buffer.
61 lines
1.3 KiB
C
61 lines
1.3 KiB
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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static inline void _reduce(fletcher16_ctx_t *ctx)
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{
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ctx->sum1 = (ctx->sum1 & 0xff) + (ctx->sum1 >> 8);
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ctx->sum2 = (ctx->sum2 & 0xff) + (ctx->sum2 >> 8);
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}
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void fletcher16_init(fletcher16_ctx_t *ctx)
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{
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ctx->sum1 = 0xff;
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ctx->sum2 = 0xff;
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}
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void fletcher16_update(fletcher16_ctx_t *ctx, const uint8_t *data, size_t len)
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{
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while (len) {
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size_t tlen = len > 20 ? 20 : len;
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len -= tlen;
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do {
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ctx->sum2 += ctx->sum1 += *data++;
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} while (--tlen);
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_reduce(ctx);
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}
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}
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uint16_t fletcher16_finish(fletcher16_ctx_t *ctx)
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{
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/* Second reduction step to reduce sums to 8 bits */
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_reduce(ctx);
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return (ctx->sum2 << 8) | ctx->sum1;
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}
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uint16_t fletcher16(const uint8_t *data, size_t bytes)
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{
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fletcher16_ctx_t ctx;
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fletcher16_init(&ctx);
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fletcher16_update(&ctx, data, bytes);
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return fletcher16_finish(&ctx);
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}
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