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98 lines
3.4 KiB
C
98 lines
3.4 KiB
C
/**
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* LDPC(255,223) Codec for TAV-DT Payloads
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*
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* Alternative to RS(255,223) with same rate (~0.875):
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* - Block size: 255 bytes (223 data + 32 parity)
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* - Uses quasi-cyclic LDPC structure for efficiency
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* - Soft-decision belief propagation decoder
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*
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* Designed as drop-in replacement for RS(255,223):
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* - Same input/output sizes
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* - Same API style
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* - Different error correction characteristics:
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* - LDPC: Better at high BER (>1e-3), gradual degradation
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* - RS: Better at low BER, hard threshold at 16 byte errors
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*
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* Created by CuriousTorvald and Claude on 2025-12-15.
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*/
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#ifndef LDPC_PAYLOAD_H
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#define LDPC_PAYLOAD_H
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#include <stdint.h>
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#include <stddef.h>
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// LDPC(255,223) parameters - matches RS(255,223) for drop-in replacement
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#define LDPC_P_BLOCK_SIZE 255 // Total codeword size (bytes)
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#define LDPC_P_DATA_SIZE 223 // Data bytes per block
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#define LDPC_P_PARITY_SIZE 32 // Parity bytes per block
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// Decoder parameters
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#define LDPC_P_MAX_ITERATIONS 30 // Maximum BP iterations
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#define LDPC_P_EARLY_TERM 1 // Enable early termination on valid codeword
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/**
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* Initialize LDPC(255,223) codec.
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* Must be called once before using encode/decode functions.
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* Thread-safe: uses static initialization.
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*/
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void ldpc_p_init(void);
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/**
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* Encode data block with LDPC(255,223).
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*
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* @param data Input data (up to LDPC_P_DATA_SIZE bytes)
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* @param data_len Length of input data (1 to LDPC_P_DATA_SIZE)
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* @param output Output buffer (must hold data_len + LDPC_P_PARITY_SIZE bytes)
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* Format: [data][parity]
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* @return Total output length (data_len + LDPC_P_PARITY_SIZE)
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*
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* Note: For data shorter than LDPC_P_DATA_SIZE, the encoder pads with zeros
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* internally but only outputs actual data + parity.
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*/
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size_t ldpc_p_encode(const uint8_t *data, size_t data_len, uint8_t *output);
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/**
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* Decode and correct LDPC(255,223) encoded block.
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*
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* @param data Buffer containing [data][parity] (modified in-place)
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* @param data_len Length of data portion (1 to LDPC_P_DATA_SIZE)
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* @return Number of iterations used (1-30), or -1 if uncorrectable
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*
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* On success, data buffer contains corrected data.
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* On failure, data buffer contents are undefined.
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*/
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int ldpc_p_decode(uint8_t *data, size_t data_len);
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/**
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* Encode data with automatic block splitting.
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* For data larger than LDPC_P_DATA_SIZE, splits into multiple blocks.
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*
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* @param data Input data
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* @param data_len Length of input data
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* @param output Output buffer (must hold ceil(data_len/223) * 255 bytes)
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* @return Total output length
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*/
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size_t ldpc_p_encode_blocks(const uint8_t *data, size_t data_len, uint8_t *output);
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/**
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* Decode data with automatic block splitting.
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*
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* @param data Buffer containing LDPC-encoded blocks (modified in-place)
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* @param total_len Total length of encoded data (multiple of LDPC_P_BLOCK_SIZE)
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* @param output Output buffer for decoded data
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* @param output_len Expected length of decoded data
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* @return Total iterations across all blocks, or -1 if any block failed
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*/
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int ldpc_p_decode_blocks(uint8_t *data, size_t total_len, uint8_t *output, size_t output_len);
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/**
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* Check if codeword is valid (syndrome check).
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*
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* @param codeword Full codeword (LDPC_P_BLOCK_SIZE bytes)
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* @return 1 if valid (zero syndrome), 0 if errors detected
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*/
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int ldpc_p_check_syndrome(const uint8_t *codeword);
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#endif // LDPC_PAYLOAD_H
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