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/*!
* \file
* \brief Implementation of a Hamming code class
* \author Tony Ottosson
*
* -------------------------------------------------------------------------
*
* IT++ - C++ library of mathematical, signal processing, speech processing,
* and communications classes and functions
*
* Copyright (C) 1995-2008 (see AUTHORS file for a list of contributors)
*
* This program 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 2 of the License, or
* (at your option) any later version.
*
* This program 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 program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* -------------------------------------------------------------------------
*/
#include <itpp/comm/hammcode.h>
#include <itpp/base/math/log_exp.h>
#include <itpp/base/converters.h>
namespace itpp {
Hamming_Code::Hamming_Code(short m)
{
n = pow2i(m) - 1;
k = pow2i(m) - m - 1;
H.set_size(n-k, n);
G.set_size(k, n);
generate_H(); // generate_H must be run before generate_G
generate_G();
}
void Hamming_Code::generate_H(void)
{
short i, j, NextPos;
char NotUsed;
bvec temp;
svec indexes(n);
indexes.zeros();
for (i=1; i<=n-k; i++) { indexes(i-1) = pow2i(n-k-i); }
NextPos = n-k;
for (i=1; i<=n; i++) {
NotUsed = 1;
for (j=0; j<n; j++)
if (i == indexes(j)) { NotUsed = 0; }
if (NotUsed) { indexes(NextPos) = i; NextPos = NextPos + 1; }
}
for (i=0; i<n; i++) {
temp = dec2bin(n-k,indexes(i)); //<-CHECK THIS OUT!!!!
for (j = 0; j < (n-k); j++) {
H(j,i) = temp(j);
}
}
}
void Hamming_Code::generate_G(void)
{
short i, j;
for (i=0; i<k; i++) {
for(j=0; j<n-k; j++)
G(i,j) = H(j,i+n-k);
}
for (i=0; i<k; i++) {
for (j=n-k; j<n; j++)
G(i,j) = 0;
}
for (i=0; i<k; i++)
G(i,i+n-k) = 1;
}
void Hamming_Code::encode(const bvec &uncoded_bits, bvec &coded_bits)
{
int length = uncoded_bits.length();
int Itterations = floor_i(static_cast<double>(length) / k);
bmat Gt = G.T();
int i;
coded_bits.set_size(Itterations * n, false);
//Code all codewords
for (i=0; i<Itterations; i++)
coded_bits.replace_mid(n*i, Gt * uncoded_bits.mid(i*k,k) );
}
bvec Hamming_Code::encode(const bvec &uncoded_bits)
{
bvec coded_bits;
encode(uncoded_bits, coded_bits);
return coded_bits;
}
void Hamming_Code::decode(const bvec &coded_bits, bvec &decoded_bits)
{
int length = coded_bits.length();
int Itterations = floor_i(static_cast<double>(length) / n);
svec Hindexes(n);
bvec temp(n-k);
bvec coded(n), syndrome(n-k);
short isynd, errorpos=0;
int i, j;
decoded_bits.set_size(Itterations*k, false);
for (i=0; i<n; i++) {
for (j=0; j<n-k; j++)
temp(j) = H(j,i);
Hindexes(i) = bin2dec(temp);
}
//Decode all codewords
for (i=0; i<Itterations; i++) {
coded = coded_bits.mid(i*n,n);
syndrome = H * coded;
isynd = bin2dec(syndrome);
if (isynd != 0) {
for (j=0; j<n; j++)
if (Hindexes(j) == isynd) { errorpos = j; };
coded(errorpos) += 1;
}
decoded_bits.replace_mid(k*i,coded.right(k));
}
}
bvec Hamming_Code::decode(const bvec &coded_bits)
{
bvec decoded_bits;
decode(coded_bits, decoded_bits);
return decoded_bits;
}
// -------------- Soft-decision decoding is not implemented ----------------
void Hamming_Code::decode(const vec &received_signal, bvec &output)
{
it_error("Hamming_Code::decode(vec, bvec); soft-decision decoding is not implemented");
}
bvec Hamming_Code::decode(const vec &received_signal)
{
it_error("Hamming_Code::decode(vec, bvec); soft-decision decoding is not implemented");
return bvec();
}
} // namespace itpp
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