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/* -*- c++ -*- */
/*
* Copyright 2002 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio 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.
*
* GNU Radio 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 GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include <atsci_reed_solomon.h>
#include <assert.h>
extern "C" {
#include "rs.h"
}
static const int rs_init_symsize = 8;
static const int rs_init_gfpoly = 0x11d;
static const int rs_init_fcr = 0; // first consecutive root
static const int rs_init_prim = 1; // primitive is 1 (alpha)
static const int rs_init_nroots = 20;
static const int N = (1 << rs_init_symsize) - 1; // 255
static const int K = N - rs_init_nroots; // 235
static const int amount_of_pad = N - ATSC_MPEG_RS_ENCODED_LENGTH; // 48
atsci_reed_solomon::atsci_reed_solomon ()
{
d_rs = init_rs_char (rs_init_symsize, rs_init_gfpoly,
rs_init_fcr, rs_init_prim, rs_init_nroots);
assert (d_rs != 0);
}
atsci_reed_solomon::~atsci_reed_solomon ()
{
if (d_rs)
free_rs_char (d_rs);
d_rs = 0;
}
void
atsci_reed_solomon::encode (atsc_mpeg_packet_rs_encoded &out, const atsc_mpeg_packet_no_sync &in)
{
unsigned char tmp[K];
assert ((int)(amount_of_pad + sizeof (in.data)) == K);
// add missing prefix zero padding to message
memset (tmp, 0, amount_of_pad);
memcpy (&tmp[amount_of_pad], in.data, sizeof (in.data));
// copy message portion to output packet
memcpy (out.data, in.data, sizeof (in.data));
// now compute parity bytes and add them to tail end of output packet
encode_rs_char (d_rs, tmp, &out.data[sizeof (in.data)]);
}
int
atsci_reed_solomon::decode (atsc_mpeg_packet_no_sync &out, const atsc_mpeg_packet_rs_encoded &in)
{
unsigned char tmp[N];
int ncorrections;
assert ((int)(amount_of_pad + sizeof (in.data)) == N);
// add missing prefix zero padding to message
memset (tmp, 0, amount_of_pad);
memcpy (&tmp[amount_of_pad], in.data, sizeof (in.data));
// correct message...
ncorrections = decode_rs_char (d_rs, tmp, 0, 0);
// copy corrected message to output, skipping prefix zero padding
memcpy (out.data, &tmp[amount_of_pad], sizeof (out.data));
return ncorrections;
}
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