#include "nist_poly.h"
#include <math.h>
#include <stddef.h>

/* Array with NIST coefficients */
/* See: https://srdata.nist.gov/its90/main/ */
double  NIST_J_d[] = {
  0.000000E+00,
  1.978425E+01,
  -2.001204E-01,
  1.036969E-02,
  -2.549687E-04,
  3.585153E-06,
  -5.344285E-08,
  5.099890E-10,
  0.000000E+00
};

/* Order of NIST polynomial */
const int count=9;


/*
 * Computes temperature by a polynomial
 */
double NIST_J_inv_poly(double voltage)
{
  double Theta=0;
  size_t i; 
  
  for (i = 0; i < count; i++) {
    Theta +=  NIST_J_d[i]*pow(voltage,i);
  }

  return Theta;

}


/*
 * Computes temperature by a product factorization.
 */
double NIST_J_inv_fact(double voltage)
{
  double Theta=0;
  double temp = 0;
  int i; 
  
  for (i = 8; i >= 0; i--) {
    temp = NIST_J_d[i] +voltage*temp;
  }

  Theta = temp;

  return Theta;

}