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