paritychecknode.c

根据LDPC码中码子的构造方法中的PEG算法

/********************************************************
 * 
 * Function node for usage on parity check function nodes.
 * Special implementation of update. 
 * Assumes that all neighbours are of size 2!
 *
 *********************************************************/
#include "ParityCheckNode.h"
#include "VariableNode.h"
#include "ParityCheck.h"
#include <iostream.h>
#include <math.h>


ParityCheckNode::ParityCheckNode(const char *name, int id, int numNeighbours) :
  FunctionNode(name, id, numNeighbours, NULL) {
}

double ParityCheckNode::LogModMinusQuan(double a) {
  double tmp;
  if(a<-3.0) tmp=0.0;
  else if(a<-0.68) tmp=-0.25*(a+3.0);
  else if(a<-0.27) tmp=-2*(a+0.97);
  else if(a<0.0) tmp=-8*(a+0.445);
  else if(a<0.15) tmp=16*a-4.0;
  else if(a<0.4) tmp=4*a-2.2;
  else if(a<1.3) tmp=2*a-1.4;
  else tmp=a-0.1;
  return(tmp);
}

double ParityCheckNode::LogModMinus(double sum, double a) {
  double tmp=LogModMinusQuan(sum+a)-LogModMinusQuan(a-sum)-sum;
  return(tmp);
}

double ParityCheckNode::jacobiFunction(double a) {
  double tmp;
  if(a>=0.0) 
    tmp=log(1.0+exp(-a));
  else 
    tmp=log(1.0+exp(a));
  return(tmp);
}

double ParityCheckNode::LogModPlus(double a, double b) {
  double tmp, jia, jian;
  jia=a+b;
  tmp=(jia>0.0)?jia:0.0;
  //tmp+=jacobiFunction(jia);
  tmp-=(a>b)?a:b;
  jian=a-b;
  //tmp-=jacobiFunction(jian);
  return(tmp);
}

/*
void ParityCheckNode::updateAll() {
  double sum=(*(VariableNode*)neighbours[0]).getOutMessage(portNumbers[0])[0];
  for(int i=1;i< numNeighbours; i++){
    sum=LogModPlus(sum, ((*(VariableNode*)neighbours[i]).getOutMessage(portNumbers[i]))[0]);
  }
  for(i=0;i< numNeighbours; i++){
    outMessages[i][0]=LogModMinus(sum, ((*(VariableNode*)neighbours[i]).getOutMessage(portNumbers[i]))[0]);
  }
}
*/

void ParityCheckNode::updateAll() {
  double *forwardMessage=new double[numNeighbours];
  double *backwardMessage = new double[numNeighbours];
  forwardMessage[0]=(*(VariableNode*)neighbours[0]).getOutMessage(portNumbers[0])[0];
  for (int i = 1; i < numNeighbours; i++){
    forwardMessage[i]=LogModPlus(forwardMessage[i-1], ((*(VariableNode*)neighbours[i]).getOutMessage(portNumbers[i]))[0]);
  }
  //backward in the internal factor graph
  backwardMessage[numNeighbours-1]=((*(VariableNode*)neighbours[numNeighbours-1]).getOutMessage(portNumbers[numNeighbours-1]))[0];
  for (i = numNeighbours-2; i >= 0; i--){
    backwardMessage[i]=LogModPlus(backwardMessage[i+1], ((*(VariableNode*)neighbours[i]).getOutMessage(portNumbers[i]))[0]);
  }
  //update the messages to the neighbours of this parity check node
  outMessages[0][0] = backwardMessage[1];
  for (i = 1; i < numNeighbours-1; i++){
    outMessages[i][0]=LogModPlus(forwardMessage[i-1], backwardMessage[i+1]);
  } 
  outMessages[numNeighbours-1][0] = forwardMessage[numNeighbours-2];

  delete [] backwardMessage;
  delete [] forwardMessage;
}
  
void ParityCheckNode::update(int port){
  //the usage of class ParityCheckNode is suitable only for 
  //function nodes where always all ports are updated at once, 
  //not only the message at one single port
  updateAll();
}

void ParityCheckNode::reset(void) {
  for (int n = 0; n < numNeighbours; n++) {
    int size = (*(VariableNode*)(neighbours[n])).getSize();
    for (int i = 0; i < size; i++) {
      outMessages[n][i] = 0.0;          //1.0/size;
    }
  }
}

void ParityCheckNode::draw(void) {
  printf("NODE: %20s, %6d\n", name, id);
  printf("---------------------------------------------\n");
  printf("PORT      NEIGHBOUR                OUTMESSAGE\n");
  for (int n = 0; n < numNeighbours; n++) {
    printf("%3d       %20s%15f\n", n, (*neighbours[n]).getName(), outMessages[n][0]);
    int size = (*(VariableNode*)(neighbours[n])).getSize();
    for (int i = 1; i < size; i++) {
      printf("%45f\n", outMessages[n][i]);
    }
  }
  printf("\n");
}

void ParityCheckNode::draw(FILE *file) {
  fprintf(file, "NODE: %20s, %6d\n", name, id);
  fprintf(file, "---------------------------------------------\n");
  fprintf(file, "PORT      NEIGHBOUR                OUTMESSAGE\n");
  for (int n = 0; n < numNeighbours; n++) {
    fprintf(file, "%3d       %20s%15f\n", n, (*neighbours[n]).getName(), outMessages[n][0]);
    int size = (*(VariableNode*)(neighbours[n])).getSize();
    for (int i = 1; i < size; i++) {
      fprintf(file, "%45f\n", outMessages[n][i]);
    }
  }
  fprintf(file, "\n");
}