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/*!
* \file
* \brief Implementation of the Extended Golay Code (24, 12, 8)
* \author Tony Ottosson
*
* -------------------------------------------------------------------------
*
* Copyright (C) 1995-2010 (see AUTHORS file for a list of contributors)
*
* This file is part of IT++ - a C++ library of mathematical, signal
* processing, speech processing, and communications classes and functions.
*
* IT++ 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 of the License, or (at your option) any
* later version.
*
* IT++ 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 IT++. If not, see <http://www.gnu.org/licenses/>.
*
* -------------------------------------------------------------------------
*/
#include <itpp/comm/egolay.h>
#include <itpp/comm/commfunc.h>
#include <itpp/base/specmat.h>
#include <itpp/base/converters.h>
namespace itpp
{
Extended_Golay::Extended_Golay(void)
{
B = "0 1 1 1 1 1 1 1 1 1 1 1;1 1 1 0 1 1 1 0 0 0 1 0;1 1 0 1 1 1 0 0 0 1 0 1;1 0 1 1 1 0 0 0 1 0 1 1;1 1 1 1 0 0 0 1 0 1 1 0;1 1 1 0 0 0 1 0 1 1 0 1;1 1 0 0 0 1 0 1 1 0 1 1;1 0 0 0 1 0 1 1 0 1 1 1;1 0 0 1 0 1 1 0 1 1 1 0;1 0 1 0 1 1 0 1 1 1 0 0;1 1 0 1 1 0 1 1 1 0 0 0;1 0 1 1 0 1 1 1 0 0 0 1";
G = concat_horizontal(eye_b(12), B);
}
void Extended_Golay::encode(const bvec &uncoded_bits, bvec &coded_bits)
{
int no_bits = uncoded_bits.length();
int no_blocks = floor_i(no_bits / 12.0);
coded_bits.set_size(24*no_blocks, false);
bmat Gt = G.T();
int i;
for (i = 0; i < no_blocks; i++)
coded_bits.replace_mid(24*i, Gt * uncoded_bits.mid(i*12, 12));
}
bvec Extended_Golay::encode(const bvec &uncoded_bits)
{
bvec coded_bits;
encode(uncoded_bits, coded_bits);
return coded_bits;
}
void Extended_Golay::decode(const bvec &coded_bits, bvec &decoded_bits)
{
int no_bits = coded_bits.length();
int no_blocks = floor_i(no_bits / 24.0);
decoded_bits.set_size(12*no_blocks, false);
int i, j;
bvec S(12), BS(12), r(12), temp(12), e(24), c(24);
bmat eyetemp = eye_b(12);
for (i = 0; i < no_blocks; i++) {
r = coded_bits.mid(i * 24, 24);
// Step 1. Compute S=G*r.
S = G * r;
// Step 2. w(S)<=3. e=(S,0). Goto 8.
if (weight(S) <= 3) {
e = concat(S, zeros_b(12));
goto Step8;
}
// Step 3. w(S+Ii)<=2. e=(S+Ii,yi). Goto 8.
for (j = 0; j < 12; j++) {
temp = S + B.get_col(j);
if (weight(temp) <= 2) {
e = concat(temp, eyetemp.get_row(j));
goto Step8;
}
}
// STEP 4. Compute B*S
BS = B * S;
// Step 5. w(B*S)<=3. e=(0,BS). Goto8.
if (weight(BS) <= 3) {
e = concat(zeros_b(12), BS);
goto Step8;
}
// Step 6. w(BS+Ri)<=2. e=(xi,BS+Ri). Goto 8.
for (j = 0; j < 12; j++) {
temp = BS + B.get_row(j);
if (weight(temp) <= 2) {
e = concat(eyetemp.get_row(j), temp);
goto Step8;
}
}
// Step 7. Uncorrectable erreor pattern. Choose the first 12 bits.
e = zeros_b(24);
goto Step8;
Step8: // Step 8. c=r+e. STOP
c = r + e;
decoded_bits.replace_mid(i*12, c.left(12));
}
}
bvec Extended_Golay::decode(const bvec &coded_bits)
{
bvec decoded_bits;
decode(coded_bits, decoded_bits);
return decoded_bits;
}
// -------------- Soft-decision decoding is not implemented ------------------
void Extended_Golay::decode(const vec &, bvec &)
{
it_error("Extended_Golay::decode(vec, bvec); soft-decision decoding is not implemented");
}
bvec Extended_Golay::decode(const vec &)
{
it_error("Extended_Golay::decode(vec, bvec); soft-decision decoding is not implemented");
return bvec();
}
} // namespace itpp
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