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/* -*- c++ -*- */
/*
* Copyright 2015 Free Software Foundation, Inc.
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation; either version 3, or (at your
* option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this software; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <ldpc_R_U_encoder_impl.h>
#include <sstream>
namespace gr {
namespace fec {
namespace code {
generic_encoder::sptr
ldpc_R_U_encoder::make(const ldpc_R_U_mtrx *H_obj)
{
return generic_encoder::sptr
(new ldpc_R_U_encoder_impl(H_obj));
}
ldpc_R_U_encoder_impl::ldpc_R_U_encoder_impl(const ldpc_R_U_mtrx *H_obj)
: generic_encoder("ldpc_R_U_encoder")
{
// LDPC parity check matrix to use for encoding
d_H = H_obj;
// Set frame size to k, the # of bits in the information word
// All buffers and settings will be based on this value.
set_frame_size(d_H->k());
}
ldpc_R_U_encoder_impl::~ldpc_R_U_encoder_impl()
{
}
int
ldpc_R_U_encoder_impl::get_output_size()
{
return d_H->n();
}
int
ldpc_R_U_encoder_impl::get_input_size()
{
return d_frame_size;
}
bool
ldpc_R_U_encoder_impl::set_frame_size(unsigned int frame_size)
{
bool ret = true;
// TODO add some bounds check here? The frame size is
// constant and specified by the size of the parity check
// matrix used for encoding.
d_frame_size = frame_size;
return ret;
}
double
ldpc_R_U_encoder_impl::rate()
{
return (d_H->n())/static_cast<double>(d_frame_size);
}
gsl_matrix*
ldpc_R_U_encoder_impl::back_solve_mod2(const gsl_matrix *U,
const gsl_matrix *y)
{
// Exploit the fact that the matrix T is upper triangular and
// sparse. In the steps to find p1 and p2, back solve rather
// than do matrix multiplication to reduce number of
// operations required.
// Form is Ux = y where U is upper triangular and y is column
// vector. Solve for x.
// Allocate memory for the result
int num_rows = (*U).size1;
int num_cols_U = (*U).size2;
gsl_matrix *x = gsl_matrix_alloc(num_rows,1);
// Back solve
for (int i = num_rows-1; i >= 0; i--) {
// x[i] = y[i]
gsl_matrix_set(x, i, 0, gsl_matrix_get(y, i, 0));
int j;
for (j = i+1; j < num_cols_U; j++) {
int U_i_j = gsl_matrix_get(U, i, j);
int x_i = gsl_matrix_get(x, i, 0);
int x_j = gsl_matrix_get(x, j, 0);
int temp1 = (U_i_j * x_j) % 2;
int temp2 = (x_i + temp1) % 2;
gsl_matrix_set(x, i, 0, temp2);
}
// Perform x[i] /= U[i,i], GF(2) operations
int U_i_i = gsl_matrix_get(U, i, i);
int x_i = gsl_matrix_get(x, i, 0);
if (x_i==0 && U_i_i==1)
gsl_matrix_set(x, i, 0, 0);
else if (x_i==0 && U_i_i==0)
gsl_matrix_set(x, i, 0, 0);
else if (x_i==1 && U_i_i==1)
gsl_matrix_set(x, i, 0, 1);
else if (x_i==1 && U_i_i==0)
std::cout << "Error in "
<< " ldpc_R_U_encoder_impl::back_solve_mod2,"
<< " division not defined.\n";
else
std::cout << "Error in ldpc_R_U_encoder_impl::back_solve_mod2\n";
}
return x;
}
void
ldpc_R_U_encoder_impl::generic_work(void *inbuffer,
void *outbuffer)
{
// Populate the information word
const unsigned char *in = (const unsigned char *)inbuffer;
unsigned int index, k = d_H->k();
gsl_matrix *s = gsl_matrix_alloc(k, 1);
for (index = 0; index < k; index++) {
double value = static_cast<double>(in[index]);
gsl_matrix_set(s, index, 0, value);
}
// Solve for p2 (parity part). By using back substitution,
// the overall complexity of determining p2 is O(n + g^2).
gsl_matrix *temp1 = d_H->mult_matrices_mod2(d_H->B(), s);
gsl_matrix *temp2 = back_solve_mod2(d_H->T(),temp1);
gsl_matrix *temp3 = d_H->mult_matrices_mod2(d_H->E(), temp2);
gsl_matrix *temp4 = d_H->mult_matrices_mod2(d_H->D(), s);
gsl_matrix *temp5 = d_H->add_matrices_mod2(temp4, temp3);
gsl_matrix *p2 = d_H->mult_matrices_mod2(
d_H->phi_inverse(), temp5);
// Solve for p1 (parity part). By using back substitution,
// the overall complexity of determining p1 is O(n).
gsl_matrix *temp6 = d_H->mult_matrices_mod2(d_H->A(), p2);
gsl_matrix *temp7 = d_H->add_matrices_mod2(temp6, temp1);
gsl_matrix *p1 = back_solve_mod2(d_H->T(),temp7);
// Populate the codeword to be output
unsigned int p1_length = (*p1).size1;
unsigned int p2_length = (*p2).size1;
unsigned char *out = (unsigned char*)outbuffer;
for (index = 0; index < p1_length; index++) {
int value = gsl_matrix_get(p1, index, 0);
out[index] = value;
}
for (index = 0; index < p2_length; index++) {
int value = gsl_matrix_get(p2, index, 0);
out[p1_length+index] = value;
}
for (index = 0; index < k; index++) {
int value = gsl_matrix_get(s, index, 0);
out[p1_length+p2_length+index] = value;
}
// Free memory
gsl_matrix_free(temp1);
gsl_matrix_free(temp2);
gsl_matrix_free(temp3);
gsl_matrix_free(temp4);
gsl_matrix_free(temp5);
gsl_matrix_free(temp6);
gsl_matrix_free(temp7);
gsl_matrix_free(p1);
gsl_matrix_free(p2);
gsl_matrix_free(s);
}
} /* namespace code */
} /* namespace fec */
} /* namespace gr */
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