YSFClients/YSFGateway/YSFFICH.cpp

/*
 *   Copyright (C) 2009-2016 by Jonathan Naylor G4KLX
 *
 *   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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "YSFConvolution.h"
#include "YSFDefines.h"
#include "Golay24128.h"
#include "YSFFICH.h"
#include "CRC.h"
#include "Log.h"

#include <cstdio>
#include <cassert>
#include <cstring>

const unsigned char BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};

#define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
#define READ_BIT1(p,i)    (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])

const unsigned int INTERLEAVE_TABLE[] = {
   0U, 40U,  80U, 120U, 160U,
   2U, 42U,  82U, 122U, 162U,
   4U, 44U,  84U, 124U, 164U,
   6U, 46U,  86U, 126U, 166U,
   8U, 48U,  88U, 128U, 168U,
  10U, 50U,  90U, 130U, 170U,
  12U, 52U,  92U, 132U, 172U,
  14U, 54U,  94U, 134U, 174U,
  16U, 56U,  96U, 136U, 176U,
  18U, 58U,  98U, 138U, 178U,
  20U, 60U, 100U, 140U, 180U,
  22U, 62U, 102U, 142U, 182U,
  24U, 64U, 104U, 144U, 184U,
  26U, 66U, 106U, 146U, 186U,
  28U, 68U, 108U, 148U, 188U,
  30U, 70U, 110U, 150U, 190U,
  32U, 72U, 112U, 152U, 192U,
  34U, 74U, 114U, 154U, 194U,
  36U, 76U, 116U, 156U, 196U,
  38U, 78U, 118U, 158U, 198U};

CYSFFICH::CYSFFICH() :
m_fich(NULL)
{
	m_fich  = new unsigned char[6U];
}

CYSFFICH::~CYSFFICH()
{
	delete[] m_fich;
}

bool CYSFFICH::decode(const unsigned char* bytes)
{
	assert(bytes != NULL);

	// Skip the sync bytes
	bytes += YSF_SYNC_LENGTH_BYTES;

	CYSFConvolution viterbi;
	viterbi.start();

	// Deinterleave the FICH and send bits to the Viterbi decoder
	for (unsigned int i = 0U; i < 100U; i++) {
		unsigned int n = INTERLEAVE_TABLE[i];
		uint8_t s0 = READ_BIT1(bytes, n) ? 1U : 0U;

		n++;
		uint8_t s1 = READ_BIT1(bytes, n) ? 1U : 0U;

		viterbi.decode(s0, s1);
	}

	unsigned char output[13U];
	viterbi.chainback(output, 96U);

	unsigned int b0 = CGolay24128::decode24128(output + 0U);
	unsigned int b1 = CGolay24128::decode24128(output + 3U);
	unsigned int b2 = CGolay24128::decode24128(output + 6U);
	unsigned int b3 = CGolay24128::decode24128(output + 9U);

	m_fich[0U] = (b0 >> 4) & 0xFFU;
	m_fich[1U] = ((b0 << 4) & 0xF0U) | ((b1 >> 8) & 0x0FU);
	m_fich[2U] = (b1 >> 0) & 0xFFU;
	m_fich[3U] = (b2 >> 4) & 0xFFU;
	m_fich[4U] = ((b2 << 4) & 0xF0U) | ((b3 >> 8) & 0x0FU);
	m_fich[5U] = (b3 >> 0) & 0xFFU;

	return CCRC::checkCCITT16(m_fich, 6U);
}

void CYSFFICH::encode(unsigned char* bytes)
{
	assert(bytes != NULL);

	// Skip the sync bytes
	bytes += YSF_SYNC_LENGTH_BYTES;

	CCRC::addCCITT16(m_fich, 6U);

	unsigned int b0 = ((m_fich[0U] << 4) & 0xFF0U) | ((m_fich[1U] >> 4) & 0x00FU);
	unsigned int b1 = ((m_fich[1U] << 8) & 0xF00U) | ((m_fich[2U] >> 0) & 0x0FFU);
	unsigned int b2 = ((m_fich[3U] << 4) & 0xFF0U) | ((m_fich[4U] >> 4) & 0x00FU);
	unsigned int b3 = ((m_fich[4U] << 8) & 0xF00U) | ((m_fich[5U] >> 0) & 0x0FFU);

	unsigned int c0 = CGolay24128::encode24128(b0);
	unsigned int c1 = CGolay24128::encode24128(b1);
	unsigned int c2 = CGolay24128::encode24128(b2);
	unsigned int c3 = CGolay24128::encode24128(b3);

	unsigned char conv[13U];
	conv[0U]  = (c0 >> 16) & 0xFFU;
	conv[1U]  = (c0 >> 8) & 0xFFU;
	conv[2U]  = (c0 >> 0) & 0xFFU;
	conv[3U]  = (c1 >> 16) & 0xFFU;
	conv[4U]  = (c1 >> 8) & 0xFFU;
	conv[5U]  = (c1 >> 0) & 0xFFU;
	conv[6U]  = (c2 >> 16) & 0xFFU;
	conv[7U]  = (c2 >> 8) & 0xFFU;
	conv[8U]  = (c2 >> 0) & 0xFFU;
	conv[9U]  = (c3 >> 16) & 0xFFU;
	conv[10U] = (c3 >> 8) & 0xFFU;
	conv[11U] = (c3 >> 0) & 0xFFU;
	conv[12U] = 0x00U;

	CYSFConvolution convolution;
	unsigned char convolved[25U];
	convolution.encode(conv, convolved, 100U);

	unsigned int j = 0U;
	for (unsigned int i = 0U; i < 100U; i++) {
		unsigned int n = INTERLEAVE_TABLE[i];

		bool s0 = READ_BIT1(convolved, j) != 0U;
		j++;

		bool s1 = READ_BIT1(convolved, j) != 0U;
		j++;

		WRITE_BIT1(bytes, n, s0);

		n++;
		WRITE_BIT1(bytes, n, s1);
	}
}

unsigned char CYSFFICH::getFI() const
{
	return (m_fich[0U] >> 6) & 0x03U;
}

unsigned char CYSFFICH::getCM() const
{
	return (m_fich[0U] >> 2) & 0x03U;
}

unsigned char CYSFFICH::getFN() const
{
	return (m_fich[1U] >> 3) & 0x07U;
}

unsigned char CYSFFICH::getFT() const
{
	return m_fich[1U] & 0x07U;
}

unsigned char CYSFFICH::getDT() const
{
	return m_fich[2U] & 0x03U;
}

void CYSFFICH::load(const unsigned char* fich)
{
	assert(fich != NULL);

	::memcpy(m_fich, fich, 4U);
}