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descramble.h
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descramble.h
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/* 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