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727 lines
21 KiB
C++
727 lines
21 KiB
C++
/*
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FILE...: mpdecode_core.c
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AUTHOR.: Matthew C. Valenti, Rohit Iyer Seshadri, David Rowe
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CREATED: Sep 2016
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C-callable core functions moved from MpDecode.c, so they can be used for
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Octave and C programs.
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*/
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#include <math.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <assert.h>
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#include "mpdecode_core.h"
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#ifndef USE_ORIGINAL_PHI0
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#include "phi0.h"
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#endif
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#ifdef __EMBEDDED__
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#include "machdep.h"
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#endif
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#define QPSK_CONSTELLATION_SIZE 4
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#define QPSK_BITS_PER_SYMBOL 2
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namespace FreeDV
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{
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/* QPSK constellation for symbol likelihood calculations */
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static COMP S_matrix[] = {
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{ 1.0f, 0.0f},
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{ 0.0f, 1.0f},
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{ 0.0f, -1.0f},
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{-1.0f, 0.0f}
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};
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// c_nodes will be an array of NumberParityBits of struct c_node
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// Each c_node contains an array of <degree> c_sub_node elements
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// This structure reduces the indexing caluclations in SumProduct()
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struct c_sub_node { // Order is important here to keep total size small.
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uint16_t index; // Values from H_rows (except last 2 entries)
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uint16_t socket; // The socket number at the v_node
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float message; // modified during operation!
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};
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struct c_node {
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int degree; // A count of elements in the following arrays
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struct c_sub_node *subs;
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};
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// v_nodes will be an array of CodeLength of struct v_node
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struct v_sub_node {
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uint16_t index; // the index of a c_node it is connected to
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// Filled with values from H_cols (except last 2 entries)
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uint16_t socket; // socket number at the c_node
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float message; // Loaded with input data
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// modified during operation!
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uint8_t sign; // 1 if input is negative
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// modified during operation!
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};
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struct v_node {
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int degree; // A count of ???
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float initial_value;
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struct v_sub_node *subs;
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};
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void encode(struct LDPC *ldpc, unsigned char ibits[], unsigned char pbits[]) {
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unsigned int tmp, par, prev=0;
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int i, p, ind;
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uint16_t *H_rows = ldpc->H_rows;
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for (p=0; p<ldpc->NumberParityBits; p++) {
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par = 0;
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for (i=0; i<ldpc->max_row_weight; i++) {
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ind = H_rows[p + i*ldpc->NumberParityBits];
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par = par + ibits[ind-1];
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}
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tmp = par + prev;
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tmp &= 1; // only retain the lsb
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prev = tmp;
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pbits[p] = tmp;
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}
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}
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#ifdef USE_ORIGINAL_PHI0
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/* Phi function */
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static float phi0(
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float x )
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{
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float z;
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if (x>10)
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return( 0 );
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else if (x< 9.08e-5 )
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return( 10 );
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else if (x > 9)
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return( 1.6881e-4 );
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/* return( 1.4970e-004 ); */
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else if (x > 8)
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return( 4.5887e-4 );
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/* return( 4.0694e-004 ); */
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else if (x > 7)
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return( 1.2473e-3 );
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/* return( 1.1062e-003 ); */
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else if (x > 6)
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return( 3.3906e-3 );
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/* return( 3.0069e-003 ); */
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else if (x > 5)
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return( 9.2168e-3 );
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/* return( 8.1736e-003 ); */
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else {
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z = (float) exp(x);
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return( (float) log( (z+1)/(z-1) ) );
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}
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}
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#endif
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/* Values for linear approximation (DecoderType=5) */
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#define AJIAN -0.24904163195436
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#define TJIAN 2.50681740420944
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/* The linear-log-MAP algorithm */
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static float max_star0(
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float delta1,
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float delta2 )
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{
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float diff;
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diff = delta2 - delta1;
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if ( diff > TJIAN )
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return( delta2 );
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else if ( diff < -TJIAN )
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return( delta1 );
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else if ( diff > 0 )
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return( delta2 + AJIAN*(diff-TJIAN) );
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else
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return( delta1 - AJIAN*(diff+TJIAN) );
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}
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void init_c_v_nodes(struct c_node *c_nodes,
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int shift,
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int NumberParityBits,
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int max_row_weight,
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uint16_t *H_rows,
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int H1,
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int CodeLength,
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struct v_node *v_nodes,
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int NumberRowsHcols,
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uint16_t *H_cols,
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int max_col_weight,
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int dec_type,
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float *input)
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{
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int i, j, k, count, cnt, c_index, v_index;
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/* first determine the degree of each c-node */
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if (shift ==0){
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for (i=0;i<NumberParityBits;i++) {
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count = 0;
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for (j=0;j<max_row_weight;j++) {
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if ( H_rows[i+j*NumberParityBits] > 0 ) {
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count++;
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}
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}
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c_nodes[i].degree = count;
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if (H1){
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if (i==0){
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c_nodes[i].degree=count+1;
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}
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else{
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c_nodes[i].degree=count+2;
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}
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}
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}
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}
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else{
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cnt=0;
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for (i=0;i<(NumberParityBits/shift);i++) {
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for (k=0;k<shift;k++){
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count = 0;
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for (j=0;j<max_row_weight;j++) {
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if ( H_rows[cnt+j*NumberParityBits] > 0 ) {
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count++;
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}
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}
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c_nodes[cnt].degree = count;
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if ((i==0)||(i==(NumberParityBits/shift)-1)){
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c_nodes[cnt].degree=count+1;
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}
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else{
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c_nodes[cnt].degree=count+2;
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}
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cnt++;
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}
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}
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}
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if (H1){
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if (shift ==0){
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for (i=0;i<NumberParityBits;i++) {
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// Allocate sub nodes
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c_nodes[i].subs = (struct c_sub_node*) calloc(c_nodes[i].degree, sizeof(struct c_sub_node));
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assert(c_nodes[i].subs);
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// Populate sub nodes
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for (j=0;j<c_nodes[i].degree-2;j++) {
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c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
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}
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j=c_nodes[i].degree-2;
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if (i==0){
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c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
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}
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else {
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c_nodes[i].subs[j].index = (CodeLength-NumberParityBits)+i-1;
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}
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j=c_nodes[i].degree-1;
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c_nodes[i].subs[j].index = (CodeLength-NumberParityBits)+i;
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}
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}
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if (shift >0){
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cnt=0;
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for (i=0;i<(NumberParityBits/shift);i++){
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for (k =0;k<shift;k++){
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// Allocate sub nodes
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c_nodes[cnt].subs = (struct c_sub_node*) calloc(c_nodes[cnt].degree, sizeof(struct c_sub_node));
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assert(c_nodes[cnt].subs);
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// Populate sub nodes
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for (j=0;j<c_nodes[cnt].degree-2;j++) {
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c_nodes[cnt].subs[j].index = (H_rows[cnt+j*NumberParityBits] - 1);
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}
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j=c_nodes[cnt].degree-2;
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if ((i ==0)||(i==(NumberParityBits/shift-1))){
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c_nodes[cnt].subs[j].index = (H_rows[cnt+j*NumberParityBits] - 1);
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}
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else{
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c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i);
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}
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j=c_nodes[cnt].degree-1;
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c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i+1);
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if (i== (NumberParityBits/shift-1))
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{
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c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i);
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}
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cnt++;
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}
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}
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}
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} else {
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for (i=0;i<NumberParityBits;i++) {
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// Allocate sub nodes
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c_nodes[i].subs = (struct c_sub_node*) calloc(c_nodes[i].degree, sizeof(struct c_sub_node));
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assert(c_nodes[i].subs);
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// Populate sub nodes
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for (j=0;j<c_nodes[i].degree;j++){
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c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
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}
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}
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}
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/* determine degree of each v-node */
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for(i=0;i<(CodeLength-NumberParityBits+shift);i++){
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count=0;
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for (j=0;j<max_col_weight;j++) {
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if ( H_cols[i+j*NumberRowsHcols] > 0 ) {
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count++;
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}
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}
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v_nodes[i].degree = count;
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}
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for(i=CodeLength-NumberParityBits+shift;i<CodeLength;i++){
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count=0;
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if (H1){
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if(i!=CodeLength-1){
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v_nodes[i].degree=2;
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} else{
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v_nodes[i].degree=1;
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}
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} else{
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for (j=0;j<max_col_weight;j++) {
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if ( H_cols[i+j*NumberRowsHcols] > 0 ) {
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count++;
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}
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}
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v_nodes[i].degree = count;
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}
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}
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if (shift>0){
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v_nodes[CodeLength-1].degree =v_nodes[CodeLength-1].degree+1;
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}
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/* set up v_nodes */
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for (i=0;i<CodeLength;i++) {
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// Allocate sub nodes
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v_nodes[i].subs = (struct v_sub_node*) calloc(v_nodes[i].degree, sizeof(struct v_sub_node));
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assert(v_nodes[i].subs);
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// Populate sub nodes
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/* index tells which c-nodes this v-node is connected to */
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v_nodes[i].initial_value = input[i];
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count=0;
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for (j=0;j<v_nodes[i].degree;j++) {
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if ((H1)&& (i>=CodeLength-NumberParityBits+shift)){
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v_nodes[i].subs[j].index=i-(CodeLength-NumberParityBits+shift)+count;
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if (shift ==0){
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count=count+1;
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}
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else{
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count=count+shift;
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}
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} else {
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v_nodes[i].subs[j].index = (H_cols[i+j*NumberRowsHcols] - 1);
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}
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/* search the connected c-node for the proper message value */
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for (c_index=0;c_index<c_nodes[ v_nodes[i].subs[j].index ].degree;c_index++)
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if ( c_nodes[ v_nodes[i].subs[j].index ].subs[c_index].index == i ) {
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v_nodes[i].subs[j].socket = c_index;
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break;
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}
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/* initialize v-node with received LLR */
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if ( dec_type == 1)
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v_nodes[i].subs[j].message = fabs(input[i]);
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else
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v_nodes[i].subs[j].message = phi0( fabs(input[i]) );
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if (input[i] < 0)
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v_nodes[i].subs[j].sign = 1;
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}
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}
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/* now finish setting up the c_nodes */
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for (i=0;i<NumberParityBits;i++) {
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/* index tells which v-nodes this c-node is connected to */
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for (j=0;j<c_nodes[i].degree;j++) {
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/* search the connected v-node for the proper message value */
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for (v_index=0;v_index<v_nodes[ c_nodes[i].subs[j].index ].degree;v_index++)
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if (v_nodes[ c_nodes[i].subs[j].index ].subs[v_index].index == i ) {
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c_nodes[i].subs[j].socket = v_index;
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break;
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}
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}
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}
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}
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///////////////////////////////////////
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/* function for doing the MP decoding */
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// Returns the iteration count
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int SumProduct( int *parityCheckCount,
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char DecodedBits[],
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struct c_node c_nodes[],
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struct v_node v_nodes[],
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int CodeLength,
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int NumberParityBits,
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int max_iter,
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float r_scale_factor,
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float q_scale_factor,
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int data[] )
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{
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(void) r_scale_factor;
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(void) q_scale_factor;
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int result;
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int bitErrors;
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int i,j, iter;
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float phi_sum;
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int sign;
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float temp_sum;
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float Qi;
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int ssum;
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result = max_iter;
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for (iter=0;iter<max_iter;iter++) {
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for(i=0; i<CodeLength; i++) DecodedBits[i] = 0; // Clear each pass!
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bitErrors = 0;
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/* update r */
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ssum = 0;
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for (j=0;j<NumberParityBits;j++) {
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sign = v_nodes[ c_nodes[j].subs[0].index ].subs[ c_nodes[j].subs[0].socket ].sign;
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phi_sum = v_nodes[ c_nodes[j].subs[0].index ].subs[ c_nodes[j].subs[0].socket ].message;
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for (i=1;i<c_nodes[j].degree;i++) {
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// Compiler should optomize this but write the best we can to start from.
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struct c_sub_node *cp = &c_nodes[j].subs[i];
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struct v_sub_node *vp = &v_nodes[ cp->index ].subs[ cp->socket ];
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phi_sum += vp->message;
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sign ^= vp->sign;
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}
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if (sign==0) ssum++;
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for (i=0;i<c_nodes[j].degree;i++) {
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struct c_sub_node *cp = &c_nodes[j].subs[i];
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struct v_sub_node *vp = &v_nodes[ cp->index ].subs[ cp->socket ];
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if ( sign ^ vp->sign ) {
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cp->message = -phi0( phi_sum - vp->message ); // *r_scale_factor;
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} else
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cp->message = phi0( phi_sum - vp->message ); // *r_scale_factor;
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}
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}
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/* update q */
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for (i=0;i<CodeLength;i++) {
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/* first compute the LLR */
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Qi = v_nodes[i].initial_value;
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for (j=0;j<v_nodes[i].degree;j++) {
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struct v_sub_node *vp = &v_nodes[i].subs[j];
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Qi += c_nodes[ vp->index ].subs[ vp->socket ].message;
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}
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/* make hard decision */
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if (Qi < 0) {
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DecodedBits[i] = 1;
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}
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/* now subtract to get the extrinsic information */
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for (j=0;j<v_nodes[i].degree;j++) {
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struct v_sub_node *vp = &v_nodes[i].subs[j];
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temp_sum = Qi - c_nodes[ vp->index ].subs[ vp->socket ].message;
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vp->message = phi0( fabs( temp_sum ) ); // *q_scale_factor;
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if (temp_sum > 0)
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vp->sign = 0;
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else
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vp->sign = 1;
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}
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}
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/* count data bit errors, assuming that it is systematic */
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for (i=0;i<CodeLength-NumberParityBits;i++)
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if ( DecodedBits[i] != data[i] )
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bitErrors++;
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/* Halt if zero errors */
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if (bitErrors == 0) {
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result = iter + 1;
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break;
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}
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// count the number of PC satisfied and exit if all OK
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*parityCheckCount = ssum;
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if (ssum==NumberParityBits) {
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result = iter + 1;
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break;
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}
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}
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return(result);
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}
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/* Convenience function to call LDPC decoder from C programs */
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int run_ldpc_decoder(struct LDPC *ldpc, uint8_t out_char[], float input[], int *parityCheckCount) {
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int max_iter, dec_type;
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float q_scale_factor, r_scale_factor;
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int max_row_weight, max_col_weight;
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int CodeLength, NumberParityBits, NumberRowsHcols, shift, H1;
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int i;
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struct c_node *c_nodes;
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struct v_node *v_nodes;
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/* default values */
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max_iter = ldpc->max_iter;
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dec_type = ldpc->dec_type;
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q_scale_factor = ldpc->q_scale_factor;
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r_scale_factor = ldpc->r_scale_factor;
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CodeLength = ldpc->CodeLength; /* length of entire codeword */
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NumberParityBits = ldpc->NumberParityBits;
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NumberRowsHcols = ldpc->NumberRowsHcols;
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char *DecodedBits = (char*) calloc( CodeLength, sizeof( char ) );
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assert(DecodedBits);
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/* derive some parameters */
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shift = (NumberParityBits + NumberRowsHcols) - CodeLength;
|
|
if (NumberRowsHcols == CodeLength) {
|
|
H1=0;
|
|
shift=0;
|
|
} else {
|
|
H1=1;
|
|
}
|
|
|
|
max_row_weight = ldpc->max_row_weight;
|
|
max_col_weight = ldpc->max_col_weight;
|
|
|
|
/* initialize c-node and v-node structures */
|
|
|
|
c_nodes = (struct c_node*) calloc( NumberParityBits, sizeof( struct c_node ) );
|
|
assert(c_nodes);
|
|
v_nodes = (struct v_node*) calloc( CodeLength, sizeof( struct v_node));
|
|
assert(v_nodes);
|
|
|
|
init_c_v_nodes(c_nodes, shift, NumberParityBits, max_row_weight, ldpc->H_rows, H1, CodeLength,
|
|
v_nodes, NumberRowsHcols, ldpc->H_cols, max_col_weight, dec_type, input);
|
|
|
|
int DataLength = CodeLength - NumberParityBits;
|
|
int *data_int = (int*) calloc( DataLength, sizeof(int) );
|
|
|
|
/* need to clear these on each call */
|
|
|
|
for(i=0; i<CodeLength; i++) DecodedBits[i] = 0;
|
|
|
|
/* Call function to do the actual decoding */
|
|
int iter = SumProduct( parityCheckCount, DecodedBits, c_nodes, v_nodes,
|
|
CodeLength, NumberParityBits, max_iter,
|
|
r_scale_factor, q_scale_factor, data_int );
|
|
|
|
for (i=0; i<CodeLength; i++) out_char[i] = DecodedBits[i];
|
|
|
|
/* Clean up memory */
|
|
|
|
free(DecodedBits);
|
|
free( data_int );
|
|
|
|
for (i=0;i<NumberParityBits;i++) {
|
|
free( c_nodes[i].subs );
|
|
}
|
|
|
|
free( c_nodes );
|
|
|
|
for (i=0;i<CodeLength;i++) {
|
|
free( v_nodes[i].subs);
|
|
}
|
|
|
|
free( v_nodes );
|
|
|
|
return iter;
|
|
}
|
|
|
|
|
|
void sd_to_llr(float llr[], double sd[], int n) {
|
|
double sum, mean, sign, sumsq, estvar, estEsN0, x;
|
|
int i;
|
|
|
|
/* convert SD samples to LLRs -------------------------------*/
|
|
|
|
sum = 0.0;
|
|
for(i=0; i<n; i++)
|
|
sum += fabs(sd[i]);
|
|
mean = sum/n;
|
|
|
|
/* find variance from +/-1 symbol position */
|
|
|
|
sum = sumsq = 0.0;
|
|
for(i=0; i<n; i++) {
|
|
sign = (sd[i] > 0.0L) - (sd[i] < 0.0L);
|
|
x = (sd[i]/mean - sign);
|
|
sum += x;
|
|
sumsq += x*x;
|
|
}
|
|
estvar = (n * sumsq - sum * sum) / (n * (n - 1));
|
|
//fprintf(stderr, "mean: %f var: %f\n", mean, estvar);
|
|
|
|
estEsN0 = 1.0/(2.0L * estvar + 1E-3);
|
|
for(i=0; i<n; i++)
|
|
llr[i] = 4.0L * estEsN0 * sd[i];
|
|
}
|
|
|
|
|
|
/*
|
|
Determine symbol likelihood from received QPSK symbols.
|
|
|
|
Notes:
|
|
|
|
1) We assume fading[] is real, it is also possible to compute
|
|
with complex fading, see CML library Demod2D.c source code.
|
|
2) Using floats instead of doubles, for stm32.
|
|
Testing shows good BERs with floats.
|
|
*/
|
|
|
|
void Demod2D(float symbol_likelihood[], /* output, M*number_symbols */
|
|
COMP r[], /* received QPSK symbols, number_symbols */
|
|
COMP S_matrix[], /* constellation of size M */
|
|
float EsNo,
|
|
float fading[], /* real fading values, number_symbols */
|
|
float mean_amp,
|
|
int number_symbols)
|
|
{
|
|
int M=QPSK_CONSTELLATION_SIZE;
|
|
int i,j;
|
|
float tempsr, tempsi, Er, Ei;
|
|
|
|
/* determine output */
|
|
|
|
for (i=0;i<number_symbols;i++) { /* go through each received symbol */
|
|
for (j=0;j<M;j++) { /* each postulated symbol */
|
|
tempsr = fading[i]*S_matrix[j].real/mean_amp;
|
|
tempsi = fading[i]*S_matrix[j].imag/mean_amp;
|
|
Er = r[i].real/mean_amp - tempsr;
|
|
Ei = r[i].imag/mean_amp - tempsi;
|
|
symbol_likelihood[i*M+j] = -EsNo*(Er*Er+Ei*Ei);
|
|
//printf("symbol_likelihood[%d][%d] = %f\n", i,j,symbol_likelihood[i*M+j]);
|
|
}
|
|
//exit(0);
|
|
}
|
|
|
|
}
|
|
|
|
|
|
void Somap(float bit_likelihood[], /* number_bits, bps*number_symbols */
|
|
float symbol_likelihood[], /* M*number_symbols */
|
|
int number_symbols)
|
|
{
|
|
int M=QPSK_CONSTELLATION_SIZE, bps = QPSK_BITS_PER_SYMBOL;
|
|
int n,i,j,k,mask;
|
|
float *num = new float[bps];
|
|
float *den = new float[bps];
|
|
float metric;
|
|
|
|
for (n=0; n<number_symbols; n++) { /* loop over symbols */
|
|
for (k=0;k<bps;k++) {
|
|
/* initialize */
|
|
num[k] = -1000000;
|
|
den[k] = -1000000;
|
|
}
|
|
|
|
for (i=0;i<M;i++) {
|
|
metric = symbol_likelihood[n*M+i]; /* channel metric for this symbol */
|
|
|
|
mask = 1 << (bps - 1);
|
|
for (j=0;j<bps;j++) {
|
|
mask = mask >> 1;
|
|
}
|
|
mask = 1 << (bps - 1);
|
|
|
|
for (k=0;k<bps;k++) { /* loop over bits */
|
|
if (mask&i) {
|
|
/* this bit is a one */
|
|
num[k] = max_star0( num[k], metric );
|
|
} else {
|
|
/* this bit is a zero */
|
|
den[k] = max_star0( den[k], metric );
|
|
}
|
|
mask = mask >> 1;
|
|
}
|
|
}
|
|
for (k=0;k<bps;k++) {
|
|
bit_likelihood[bps*n+k] = num[k] - den[k];
|
|
}
|
|
}
|
|
|
|
delete[] den;
|
|
delete[] num;
|
|
}
|
|
|
|
|
|
void symbols_to_llrs(float llr[], COMP rx_qpsk_symbols[], float rx_amps[], float EsNo, float mean_amp, int nsyms) {
|
|
int i;
|
|
|
|
float *symbol_likelihood = new float[nsyms*QPSK_CONSTELLATION_SIZE];
|
|
float *bit_likelihood = new float[nsyms*QPSK_BITS_PER_SYMBOL];
|
|
|
|
Demod2D(symbol_likelihood, rx_qpsk_symbols, S_matrix, EsNo, rx_amps, mean_amp, nsyms);
|
|
Somap(bit_likelihood, symbol_likelihood, nsyms);
|
|
for(i=0; i<nsyms*QPSK_BITS_PER_SYMBOL; i++) {
|
|
llr[i] = -bit_likelihood[i];
|
|
}
|
|
|
|
delete[] bit_likelihood;
|
|
delete[] symbol_likelihood;
|
|
}
|
|
|
|
void ldpc_print_info(struct LDPC *ldpc) {
|
|
fprintf(stderr, "ldpc->max_iter = %d\n", ldpc->max_iter);
|
|
fprintf(stderr, "ldpc->dec_type = %d\n", ldpc->dec_type);
|
|
fprintf(stderr, "ldpc->q_scale_factor = %d\n", ldpc->q_scale_factor);
|
|
fprintf(stderr, "ldpc->r_scale_factor = %d\n", ldpc->r_scale_factor);
|
|
fprintf(stderr, "ldpc->CodeLength = %d\n", ldpc->CodeLength);
|
|
fprintf(stderr, "ldpc->NumberParityBits = %d\n", ldpc->NumberParityBits);
|
|
fprintf(stderr, "ldpc->NumberRowsHcols = %d\n", ldpc->NumberRowsHcols);
|
|
fprintf(stderr, "ldpc->max_row_weight = %d\n", ldpc->max_row_weight);
|
|
fprintf(stderr, "ldpc->max_col_weight = %d\n", ldpc->max_col_weight);
|
|
fprintf(stderr, "ldpc->data_bits_per_frame = %d\n", ldpc->data_bits_per_frame);
|
|
fprintf(stderr, "ldpc->coded_bits_per_frame = %d\n", ldpc->coded_bits_per_frame);
|
|
fprintf(stderr, "ldpc->coded_syms_per_frame = %d\n", ldpc->coded_syms_per_frame);
|
|
}
|
|
|
|
} // FreeDV
|
|
|
|
/* vi:set ts=4 et sts=4: */
|