Working TAV-DT encoder/decoder

video_encoder/lib/libfec/reed_solomon.h

@@ -0,0 +1,82 @@
+/**
+ * Reed-Solomon (255,223) Codec for TAV-DT
+ *
+ * Standard RS code over GF(2^8):
+ * - Block size: 255 bytes (223 data + 32 parity)
+ * - Error correction: up to 16 byte errors
+ * - Error detection: up to 32 byte errors
+ *
+ * Uses primitive polynomial: x^8 + x^4 + x^3 + x^2 + 1 (0x11D)
+ * Generator polynomial: g(x) = product of (x - alpha^i) for i = 0..31
+ *
+ * Created by CuriousTorvald and Claude on 2025-12-09.
+ */
+
+#ifndef REED_SOLOMON_H
+#define REED_SOLOMON_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+// RS(255,223) parameters
+#define RS_BLOCK_SIZE     255   // Total codeword size
+#define RS_DATA_SIZE      223   // Data bytes per block
+#define RS_PARITY_SIZE    32    // Parity bytes per block (2t = 32, t = 16)
+#define RS_MAX_ERRORS     16    // Maximum correctable errors (t)
+
+/**
+ * Initialize Reed-Solomon codec.
+ * Must be called once before using encode/decode functions.
+ * Thread-safe: uses static initialization.
+ */
+void rs_init(void);
+
+/**
+ * Encode data block with Reed-Solomon parity.
+ *
+ * @param data      Input data (up to RS_DATA_SIZE bytes)
+ * @param data_len  Length of input data (1 to RS_DATA_SIZE)
+ * @param output    Output buffer (must hold data_len + RS_PARITY_SIZE bytes)
+ *                  Format: [data][parity]
+ * @return          Total output length (data_len + RS_PARITY_SIZE)
+ *
+ * Note: For data shorter than RS_DATA_SIZE, the encoder pads with zeros
+ * internally but only outputs actual data + parity.
+ */
+size_t rs_encode(const uint8_t *data, size_t data_len, uint8_t *output);
+
+/**
+ * Decode and correct Reed-Solomon encoded block.
+ *
+ * @param data      Buffer containing [data][parity] (modified in-place)
+ * @param data_len  Length of data portion (1 to RS_DATA_SIZE)
+ * @return          Number of errors corrected (0-16), or -1 if uncorrectable
+ *
+ * On success, data buffer contains corrected data (parity may also be corrected).
+ * On failure, data buffer contents are undefined.
+ */
+int rs_decode(uint8_t *data, size_t data_len);
+
+/**
+ * Encode data with automatic block splitting.
+ * For data larger than RS_DATA_SIZE, splits into multiple RS blocks.
+ *
+ * @param data        Input data
+ * @param data_len    Length of input data
+ * @param output      Output buffer (must hold ceil(data_len/223) * 255 bytes)
+ * @return            Total output length
+ */
+size_t rs_encode_blocks(const uint8_t *data, size_t data_len, uint8_t *output);
+
+/**
+ * Decode data with automatic block splitting.
+ *
+ * @param data        Buffer containing RS-encoded blocks (modified in-place)
+ * @param total_len   Total length of encoded data (multiple of RS_BLOCK_SIZE)
+ * @param output      Output buffer for decoded data
+ * @param output_len  Expected length of decoded data
+ * @return            Total errors corrected across all blocks, or -1 if any block failed
+ */
+int rs_decode_blocks(uint8_t *data, size_t total_len, uint8_t *output, size_t output_len);
+
+#endif // REED_SOLOMON_H