/* descramble.h */

// Functions for processing the radio-header:
// descramble
// deinterleave
// FECdecoder

// (C) 2011 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; version 2 of the License.
 *
 *	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.
 */
 
// This code was originally written by JOnathan Naylor, G4KLX, as part
// of the "pcrepeatercontroller" project
// More info:
// http://groups.yahoo.com/group/pcrepeatercontroller



// Changes:
// Convert C++ to C

// Version 20111106: initial release




#include <stdio.h>
#include <string.h>

// function traceBack
int traceBack (int * out, int * m_pathMemory0, int * m_pathMemory1, int * m_pathMemory2, int * m_pathMemory3) {
	enum FEC_STATE { S0, S1, S2, S3 } state;
	int loop;
	int length=0;

	state=S0;

	for (loop=329; loop >= 0; loop--, length++) {

		switch (state) {
			case S0: // if state S0
				if (m_pathMemory0[loop]) {
					state = S2; // lower path
				} else {
					state = S0; // upper path
				}; // end else - if
				out[loop]=0;
				break;
			
			case S1: // if state S1
				if (m_pathMemory1[loop]) {
					state = S2; // lower path
				} else {
					state = S0; // upper path
				}; // end else - if
				out[loop]=1;
				break;
			
			case S2: // if state S2
				if (m_pathMemory2[loop]) {
					state = S3; // lower path
				} else {
					state = S1; // upper path
				}; // end else - if
				out[loop]=0;
				break;
			
			case S3: // if state S3
				if (m_pathMemory3[loop]) {
					state = S3; // lower path
				} else {
					state = S1; // upper path
				}; // end else - if
				out[loop]=1;
				break;
			
		}; // end switch
	}; // end for

return(length);
}; // end function



// function viterbiDecode

void viterbiDecode (int n, int *data, int *m_pathMemory0, int *m_pathMemory1, int *m_pathMemory2, int *m_pathMemory3, int *m_pathMetric) {
	int tempMetric[4];
	int metric[8];
	int loop;

	int m1;
	int m2;

	metric[0]=(data[1]^0)+(data[0]^0);
	metric[1]=(data[1]^1)+(data[0]^1);
	metric[2]=(data[1]^1)+(data[0]^0);
	metric[3]=(data[1]^0)+(data[0]^1);
	metric[4]=(data[1]^1)+(data[0]^1);
	metric[5]=(data[1]^0)+(data[0]^0);
	metric[6]=(data[1]^0)+(data[0]^1);
	metric[7]=(data[1]^1)+(data[0]^0);

	// Pres. state = S0, Prev. state = S0 & S2
	m1=metric[0]+m_pathMetric[0];
	m2=metric[4]+m_pathMetric[2];
	if (m1<m2) {
		m_pathMemory0[n]=0;
		tempMetric[0]=m1;
	} else {
		m_pathMemory0[n]=1;
		tempMetric[0]=m2;
	}; // end else - if

	// Pres. state = S1, Prev. state = S0 & S2
	m1=metric[1]+m_pathMetric[0];
	m2=metric[5]+m_pathMetric[2];
	if (m1<m2) {
		m_pathMemory1[n]=0;
		tempMetric[1]=m1;
	} else {
		m_pathMemory1[n]=1;
		tempMetric[1]=m2;
	}; // end else - if

	// Pres. state = S2, Prev. state = S2 & S3
	m1=metric[2]+m_pathMetric[1];
	m2=metric[6]+m_pathMetric[3];
	if (m1<m2) {
		m_pathMemory2[n]=0;
		tempMetric[2]=m1;
	} else {
		m_pathMemory2[n]=1;
		tempMetric[2]=m2;
	}

	// Pres. state = S3, Prev. state = S1 & S3
	m1=metric[3]+m_pathMetric[1];
	m2=metric[7]+m_pathMetric[3];
	if (m1 < m2) {
		m_pathMemory3[n]=0;
		tempMetric[3]=m1;
	} else {
		m_pathMemory3[n]=1;
		tempMetric[3]=m2;
	}; // end else - if

	for (loop=0;loop<4;loop++) {
		m_pathMetric[loop]=tempMetric[loop];
	}; // end for

}; // end function ViterbiDecode


// function FECdecoder 
// returns outlen
int FECdecoder (int * in, int * out) {
int outLen;

int m_pathMemory0[330]; memset(m_pathMemory0,0,330*sizeof(int));
int m_pathMemory1[330]; memset(m_pathMemory1,0,330*sizeof(int));
int m_pathMemory2[330]; memset(m_pathMemory2,0,330*sizeof(int));
int m_pathMemory3[330]; memset(m_pathMemory3,0,330*sizeof(int));
int m_pathMetric[4];

int loop,loop2;

int n=0;

for (loop=0;loop<4;loop++) {
	m_pathMetric[loop]=0;
}; // end for


for (loop2=0;loop2<660;loop2+=2, n++) {
	int data[2];

	if (in[loop2]) {
		data[1]=1;
	} else {
		data[1]=0;
	}; // end else - if

	if (in[loop2+1]) {
		data[0]=1;
	} else {
		data[0]=0;
	}; // end else - if

	viterbiDecode(n, data, m_pathMemory0, m_pathMemory1, m_pathMemory2, m_pathMemory3, m_pathMetric);
}; // end for

outLen=traceBack(out, m_pathMemory0, m_pathMemory1, m_pathMemory2, m_pathMemory3);

// Swap endian-ness
// code removed (done converting bits into octets), done in main program

//for (loop=0;loop<330;loop+=8) {
//	int temp;
//	temp=out[loop];out[loop]=out[loop+7];out[loop+7]=temp;
//	temp=out[loop+1];out[loop+1]=out[loop+6];out[loop+6]=temp;
//	temp=out[loop+2];out[loop+2]=out[loop+5];out[loop+5]=temp;
//	temp=out[loop+3];out[loop+3]=out[loop+4];out[loop+4]=temp;
//}

return(outLen);

}; // end function FECdecoder


// function deinterleave
void deinterleave (int * in, int * out) {

int k=0;
int loop=0;
// function starts here

// init vars
k=0;

for (loop=0;loop<660;loop++) {
	out[k]=in[loop];

	k += 24;

	if (k >= 672) {
		k -= 671;
	} else if (k >= 660) {
		k -= 647;
	}; // end elsif - if
}; // end for

}; // end function deinterleave



/// function scramble

void scramble (int * in,int * out) {

static const int SCRAMBLER_TABLE_BITS[] = {
	0,0,0,0,1,1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,
	0,0,1,0,0,1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,
	1,1,0,1,0,1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0,1,0,0,0,0,1,0,1,0,1,0,
	1,1,1,1,1,0,1,0,0,1,0,1,0,0,0,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,1,0,
	0,0,0,1,1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,0,
	0,1,0,0,1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,1,
	1,0,1,0,1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0,1,0,0,0,0,1,0,1,0,1,0,1,
	1,1,1,1,0,1,0,0,1,0,1,0,0,0,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,1,0,0,
	0,0,1,1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,0,0,
	1,0,0,1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,1,1,
	0,1,0,1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0,1,0,0,0,0,1,0,1,0,1,0,1,1,
	1,1,1,0,1,0,0,1,0,1,0,0,0,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,1,0,0,0,
	0,1,1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,0,0,1,
	0,0,1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,1,1,0,
	1,0,1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0,1,0,0,0,0,1,0,1,0,1,0,1,1,1,
	1,1,0,1,0,0,1,0,1,0,0,0,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,1,0,0,0,0,
	1,1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,0,0,1,0,
	0,1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,1,1,0,1,
	0,1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0,1,0,0,0,0,1,0,1,0,1,0,1,1,1,1,
	1,0,1,0,0,1,0,1,0,0,0,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,1,0,0,0,0,1,
	1,1,0,1,1,1,1,0,0,1,0,1,1,0,0,1,0,0,1,0,0,0,0,0,0,1,0,0,0,1,0,0,
	1,1,0,0,0,1,0,1,1,1,0,1,0,1,1,0,1,1,0,0,0,0,0,1,1,0,0,1,1,0,1,0,
	1,0,0,1,1,1,0,0,1,1,1,1,0,1,1,0};

const int SCRAMBLER_TABLE_BITS_LENGTH=720;

int loop=0;
int m_count=0;


for (loop=0; loop < 660; loop++) {
	out[loop] = in[loop] ^ SCRAMBLER_TABLE_BITS[m_count++];

	if (m_count >= SCRAMBLER_TABLE_BITS_LENGTH) {
		m_count = 0U;
	}; // end if
}; // end for

}; // end function scramble