#include <stddef.h>
#include <stdint.h>

Typedefs
typedef struct rs_context	rs_context
	Opaque Reed-Solomon codec context.

Functions
rs_context *	rs_create (uint16_t K, uint16_t M)
	Create a Reed-Solomon codec for RS(K, M) over GF(2^8).
void	rs_free (rs_context *ctx)
	Free a Reed-Solomon codec context.
uint8_t	rs_get_coefficient (const rs_context *ctx, uint16_t m, uint16_t k)
	Get the generator matrix coefficient for parity shard m, data shard k.
void	rs_encode_incremental (uint8_t coeff, const uint8_t data, uint8_t parity, size_t shard_size)
	Incrementally accumulate one data shard's contribution to one parity shard.
int	rs_decode (const rs_context ctx, uint8_t shards, const uint8_t present, size_t shard_size)
	Decode (reconstruct) erased shards.

Typedef Documentation

◆ rs_context

typedef struct rs_context rs_context

Opaque Reed-Solomon codec context.

Definition at line 28 of file reed_solomon.h.

Function Documentation

◆ rs_create()

rs_context * rs_create	(	uint16_t	K,
		uint16_t	M )

Create a Reed-Solomon codec for RS(K, M) over GF(2^8).

K = number of data shards, M = number of parity shards. K + M must be <= 255 (GF(2^8) field size minus 1).

The codec precomputes the Vandermonde-derived generator matrix (M rows x K columns) used for encoding.

Parameters

K	Number of data shards (>= 1).
M	Number of parity shards (>= 1).

Returns: Codec context, or NULL on error.

Definition at line 150 of file reed_solomon.c.

References build_vandermonde(), rs_context::coding, rs_context::gen, gf256_mul(), invert_matrix(), rs_context::K, rs_context::M, and rs_create().

Referenced by aaruf_set_erasure_coding(), ec_load_ecmb(), ec_recover_raw_block(), ec_write_batch_parity(), and rs_create().

◆ rs_decode()

int rs_decode	(	const rs_context *	ctx,
		uint8_t **	shards,
		const uint8_t *	present,
		size_t	shard_size )

Decode (reconstruct) erased shards.

Given K+M shards where some are erased, reconstruct the erased ones using Gaussian elimination over GF(2^8).

Parameters

ctx	Codec context.
shards	Array of K+M shard pointers (each shard_size bytes). Erased shards must point to allocated buffers of shard_size bytes (content will be overwritten).
present	Boolean array of K+M entries: 1 = shard is valid, 0 = shard is erased.
shard_size	Number of bytes per shard.

Returns: 0 on success, -1 if too many erasures (> M), -2 on allocation failure.

Definition at line 218 of file reed_solomon.c.

References rs_context::coding, gf256_mul(), gf256_mul_region(), invert_matrix(), rs_context::K, rs_context::M, and rs_decode().

Referenced by ec_recover_data_block(), ec_recover_raw_block(), and rs_decode().

◆ rs_encode_incremental()

void rs_encode_incremental	(	uint8_t	coeff,
		const uint8_t *	data,
		uint8_t *	parity,
		size_t	shard_size )

Incrementally accumulate one data shard's contribution to one parity shard.

Computes: parity[i] ^= GF_mul(data[i], coeff) for all i in [0, shard_size).

This is the core primitive for streaming write: for each data block written, call this M times (once per parity shard) with the appropriate coefficient.

For M=1 (XOR-only), coeff is always 1, and this reduces to XOR.

Parameters

coeff	GF(2^8) coefficient from rs_get_coefficient().
data	Data shard bytes (read-only, shard_size bytes).
parity	Parity shard accumulator (read-write, shard_size bytes, must be zeroed before first call).
shard_size	Number of bytes per shard.

Definition at line 213 of file reed_solomon.c.

References gf256_mul_region(), and rs_encode_incremental().

Referenced by ec_accumulate_data_block(), ec_write_batch_parity(), and rs_encode_incremental().