function limit (a,b,c)
{
// a and c must not be NaN
// if b is NaN, NaN is returned
  if (!(c >= a)) {
    alert ("internal ERROR in cap (a,b,c): a = " + a + " ; b = " + b + " ; c = " + c) ;
    return 0 ;
  }
  if (b < a) return a ;
  if (b > c) return c ;
  return b ;
}

function f_biv ()
{
// Read input parameters from form
  var Year = limit (2012, parseInt (document.getElementById("biv_form").Year.value), 2020) ;
  var CO2 = limit (0, parseInt (document.getElementById("biv_form").CO2.value), 500) ;
  var Factor = limit (0, parseFloat (document.getElementById("biv_form").Factor.value), 2.0) ;
  var Euro = limit (0, parseInt (document.getElementById("biv_form").Euro.value), 6) ;
  var Filter = document.getElementById("biv_form").Filter.checked ;
  var Diesel = document.getElementById("biv_form").Diesel.checked ;

  if (Filter && Diesel) {
    if (Euro == 4) {
      Euro = 5
    }
    if (Euro == 3) {
      Euro = 4
    }
  }

  var c = 0 ;

  if (Diesel) {
    switch (Euro) {
      case (0):
        c = 8521.27;
        break ;
      case (1):
        c = 2500.00;
        break ;
      case (2):
        c = 1813.47 ;
        break ;
      case (3):
        c = 731.42 ;
        break ;
      case (4):
        c = 190.89 ;
        break ;
      case (5):
        c = 93.72 ;
        break ;
      case (6):
        c = 49.01
        break ;
    }
  }
  else {
    switch (Euro) {
      case (0):
        c = 3389.22;
        break ;
      case (1):
        c = 1515.70;
        break ;
      case (2):
        c = 453.24;
        break ;
      case (3):
        c = 284.31;
        break ;
      case (4):
        c = 68.26;
        break ;
      case (5):
        c = 61.35;
        break ;
      case (6):
        c = 61.35;
        break ;
    }
  }

  var x ;

  switch (Year) {
    case 2012:
      x = 0 ;
      break ;
    case 2013:
      x = 4.5 ;
      break ;
    case 2014:
      x = 9.0 ;
      break ;
    case 2015:
      x = 13.5 ;
      break ;
    default:
      x = 0 ;
  }

  var base ;
  base = ((CO2*Factor) + x) / 250.0
  var power2, power6 ;
  power2 = base * base ;
  power6 = power2 * power2 * power2;
  
  var result ;
  result = ((power6 * 6000.0) + c) ;
  document.getElementById("biv_form").BIV.value = result.toFixed(2) ;
}