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94 lines
3.0 KiB
C
94 lines
3.0 KiB
C
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/*
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* Copyright (C) 2021 Benjamin Valentin <benjamin.valentin@ml-pa.com>
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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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* @defgroup sys_coding_xor XOR code
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* @ingroup sys_coding
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* @brief Simple XOR based coding algorithms
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*
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* @experimental This is a very basic implementation, it can only recover
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* 1 lost block in 3 and only has a 33% chance of recovering
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* two consecutive lost blocks.
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* API / Algorithm might change if that means we can do better.
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*
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* @{
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*
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* @file
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* @brief XOR coding definitions
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*
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* @author Benjamin Valentin <benjamin.valentin@ml-pa.com>
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*/
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#ifndef CODING_XOR_H
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#define CODING_XOR_H
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#include <stddef.h>
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#include <stdint.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @brief Number of payload bytes per parity byte
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*/
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#ifndef CONFIG_CODING_XOR_CHECK_BYTES
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#define CONFIG_CODING_XOR_CHECK_BYTES 3U
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#endif
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/**
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* @brief Get the size of the needed parity buffer for a given payload size
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*
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* @param in Payload length
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*/
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#define CODING_XOR_PARITY_LEN(in) (((in) + CONFIG_CODING_XOR_CHECK_BYTES - 1) \
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/ CONFIG_CODING_XOR_CHECK_BYTES)
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/**
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* @brief Generate parity and mix data buffer
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*
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* This generates parity data to recover one in @ref CONFIG_CODING_XOR_CHECK_BYTES
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* bytes.
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* The data buffer is then mixed to distribute bytes amongst transfer blocks, so
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* that the chance for consecutive bytes to be in the same block is lowered.
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*
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* @param[in,out] data The data buffer to be processed
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* @param[in] len Size of the data buffer
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* @param[out] parity Buffer to hold parity data.
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* Must be at least `CODING_XOR_PARITY_LEN(len)` bytes
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*/
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void coding_xor_generate(void *data, size_t len, uint8_t *parity);
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/**
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* @brief Restore and unmix buffer
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*
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*
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* @param[in, out] data The data buffer to be restored
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* @param[in] len Size of the data buffer
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* @param[in,out] parity Buffer with parity data.
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* Must be at least `CODING_XOR_PARITY_LEN(len)` bytes
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* @param[in,out] blocks Bitfieled to indicate which blocks were received.
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* This indicates the presence of both data and parity
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* blocks. Parity blocks are appended after the last
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* data block.
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* If a block was restored it's bit will be set.
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* @param[in] block_size Size of a data/payload block
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* @param[in] recover_parity If true, missing parity blocks will be re-generated
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* from data blocks.
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*
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* @return True if all data blocks were recovered
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*/
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bool coding_xor_recover(void *data, size_t len, uint8_t *parity,
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uint8_t *blocks, size_t block_size, bool recover_parity);
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#ifdef __cplusplus
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}
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#endif
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#endif /* CODING_XOR_H */
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/** @} */
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