fec.c File Reference

Forward error correction based on Vandermonde matrices. More...

#include <regex.h>
#include "para.h"
#include "error.h"
#include "portable_io.h"
#include "string.h"
#include "fec.h"

Macros
#define	GF_BITS   8
	Code over GF(256). More...
#define	GF_SIZE   ((1 << GF_BITS) - 1)
	The largest number in GF(256) More...
#define	gf_mul(x, y)   gf_mul_table[x][y]
	Multiply two GF numbers. More...
#define	UNROLL   16
	How often the loop is unrolled. More...
#define	FEC_SWAP(a, b)   {typeof(a) tmp = a; a = b; b = tmp;}
	Swap two numbers. More...

Functions
void	fec_free (struct fec_parms *p)
	Deallocate a fec params structure. More...
int	fec_new (int k, int n, struct fec_parms **result)
	Create a new encoder and return an opaque descriptor to it. More...
void	fec_encode (struct fec_parms *parms, const unsigned char *const *src, unsigned char *dst, int idx, int sz)
	Compute one encoded slice of the given input. More...
int	fec_decode (struct fec_parms *parms, unsigned char **data, int *idx, int sz)
	Decode one slice from the group of received slices. More...

Detailed Description

Forward error correction based on Vandermonde matrices.

Macro Definition Documentation

GF_BITS

#define GF_BITS   8

Code over GF(256).

GF_SIZE

#define GF_SIZE   ((1 << GF_BITS) - 1)

The largest number in GF(256)

gf_mul

#define gf_mul	(		x,
			y
	)		gf_mul_table[x][y]

Multiply two GF numbers.

UNROLL

#define UNROLL   16

How often the loop is unrolled.

FEC_SWAP

#define FEC_SWAP	(		a,
			b
	)		{typeof(a) tmp = a; a = b; b = tmp;}

Swap two numbers.

Function Documentation

fec_free()

void fec_free

(

struct fec_parms *

p

)

Deallocate a fec params structure.

Parameters

p	The structure to free.

fec_new()

int fec_new	(	int	k,
		int	n,
		struct fec_parms **	result
	)

Create a new encoder and return an opaque descriptor to it.

Parameters

k	Number of input slices.
n	Number of output slices.
result	On success the Fec descriptor is returned here.

Returns

Standard.

This creates the k*n encoding matrix. It is computed starting with a Vandermonde matrix, and then transformed into a systematic matrix.

fec_encode()

void fec_encode	(	struct fec_parms *	parms,
		const unsigned char *const *	src,
		unsigned char *	dst,
		int	idx,
		int	sz
	)

Compute one encoded slice of the given input.

Parameters

parms	The fec parameters returned earlier by fec_new().
src	The k data slices to encode.
dst	Result pointer.
idx	The index of the slice to compute.
sz	The size of the input data packets.

Encode the k slices of size sz given by src and store the output slice number idx in dst.

fec_decode()

int fec_decode	(	struct fec_parms *	parms,
		unsigned char **	data,
		int *	idx,
		int	sz
	)

Decode one slice from the group of received slices.

Parameters

parms	Pointer to fec params structure.
data	Pointers to received packets.
idx	Pointer to packet indices (gets modified).
sz	Size of each packet.

Returns

Zero on success, -1 on errors.

The data vector of received slices and the indices of slices are used to produce the correct output slice. The data slices are modified in-place.