lookup.c

This a framework to test new ideas in transmission technology. Actual development is a LDPC-coder in

#include "lookup.h"
#include <math.h>
#if OPTIMIZE
# define size 53
#define STEP_SIZE 1
#define MAX_VALUE 26
//#define size (2*MAX_VALUE)/STEP_SIZE + 1
//const int size = (2* MAX_VALUE) / STEP_SIZE + 1;
double val[size];
// Lookup-table functions for log and exp.
double lookup_exp( double x ) {
  int i;
  i=(int)((x+MAX_VALUE)/STEP_SIZE);
  if(i>size-1)
    return val[size-1];
  else
    if(i<0)
      return val[0];
  return val[i];
}


double lookup_log( double x ) {
  int temp,min=0,max=size-1;
  while(1) {
    temp=(min+max)/2;
    if(temp==max || temp==min)
      break;
    if(val[temp]<=x && x <val[temp+1])
      break;
    else
      if(val[temp+1]<=x)
        min=temp+1;
      else
        max=temp;
  }
  return temp*STEP_SIZE-MAX_VALUE;
}


// Initialisation function where you can set up some
// look-up tables using the math.h functions
void lookup_init() {

  int i=0;
  //exp = (double *) swr_malloc(sizeof(double) * size);
  for(;i<size;i++)
    val[i]=exp( (-1 * MAX_VALUE) + (i* STEP_SIZE) );
}


// Clean up the tables, that is, free eventually allocated
// memory
void lookup_exit() {
  //swr_free(exp);
}

#endif