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fec_imp.h  view on Meta::CPAN

    b = NEW_GF_MATRIX(1, k);

    p = NEW_GF_MATRIX(1, k);
   
    for ( j=1, i = 0 ; i < k ; i++, j+=k ) {
	c[i] = 0 ;
	p[i] = src[j] ;    /* p[i] */
    }
    /*
     * construct coeffs. recursively. We know c[k] = 1 (implicit)
     * and start P_0 = x - p_0, then at each stage multiply by
     * x - p_i generating P_i = x P_{i-1} - p_i P_{i-1}
     * After k steps we are done.
     */
    c[k-1] = p[0] ;	/* really -p(0), but x = -x in GF(2^m) */
    for (i = 1 ; i < k ; i++ ) {
	gf p_i = p[i] ; /* see above comment */
	for (j = k-1  - ( i - 1 ) ; j < k-1 ; j++ )
	    c[j] ^= gf_mul( p_i, c[j+1] ) ;
	c[k-1] ^= p_i ;
    }

fec_imp.h  view on Meta::CPAN

    DDB(fprintf(stderr, "generate_gf took %ldus\n", ticks[0]);)
    TICK(ticks[0]);
    init_mul_table();
    TOCK(ticks[0]);
    DDB(fprintf(stderr, "init_mul_table took %ldus\n", ticks[0]);)
    fec_initialized = 1 ;
}

/*
 * This section contains the proper FEC encoding/decoding routines.
 * The encoding matrix is computed starting with a Vandermonde matrix,
 * and then transforming it into a systematic matrix.
 */

struct fec_parms {
    int k, n ;		/* parameters of the code */
    gf *enc_matrix ;
} ;

void
fec_free(struct fec_parms *p)

fec_imp.h  view on Meta::CPAN

	fprintf(stderr, "Invalid parameters k %d n %d GF_SIZE %d\n",
		k, n, GF_SIZE );
	return NULL ;
    }
    retval = my_malloc(sizeof(struct fec_parms), "new_code");
    retval->k = k ;
    retval->n = n ;
    retval->enc_matrix = NEW_GF_MATRIX(n, k);
    tmp_m = NEW_GF_MATRIX(n, k);
    /*
     * fill the matrix with powers of field elements, starting from 0.
     * The first row is special, cannot be computed with exp. table.
     */
    tmp_m[0] = 1 ;
    for (col = 1; col < k ; col++)
	tmp_m[col] = 0 ;
    for (p = tmp_m + k, row = 0; row < n-1 ; row++, p += k) {
	for ( col = 0 ; col < k ; col ++ )
	    p[col] = gf_exp[modnn(row*col)];
    }