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>
#include "spc.h"

#if OPTIMIZE
#define STEP_SIZE 0.001
#define ASTEP_SIZE 0.001
#define AMAX_VALUE 1
#define tsize 2*T+1
#define asize 2*TA+1
#define DBG_LVL 2
short int tval[tsize];
short int aval[asize];

double restrict(double x,int MAX) {
  if(x<MAX && x>-1*MAX)
    return x;
  if(x>MAX)
    return MAX;
  if(x<-1*MAX)
    return -1*MAX;
  return 0;
}


/* Initialisation function where the lookup tables are
 * set up using math functions
 */

void lookup_init() {
  double value;
  int i=0;
  for(i=0;i<tsize;i++)
    tval[i]=(short int)((double)TA*tanh((double)(i-T)*MAX_VALUE/(2*T)));
  for(i=1;i<asize-1;i++) {
    value = 2*((double)T/MAX_VALUE*atanh((double)(i-TA)/(TA)));
    if(value>T)
      value = T;
    if(value<-T)
      value = -T;

    aval[i] = (short int)(value);

  }
  aval[0]=-T;
  aval[2*TA]=T;
}

short int lookup_tanh( int x ) {
  return tval[x+T];
}

short int lookup_atanh( int x ) {
  return aval[x+TA];
}

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

#endif