function cal_thr(age, il, gen) {
   
   if (gen == "F") {
		if (il == "cardio") {
			thr = (226 - age) * 0.6;
		} else {
			thr = (226 - age) * 0.8;
		}
   } else {
		if (il == "cardio") {
			thr = (220 - age) * 0.6;
		} else {
			thr = (220 - age) * 0.8;
		}
   }
   
   return thr;
}

function compute() {
   var f = document.thr_input;
   var il = f.il.options[f.il.selectedIndex].value;
   var gen = f.gen.options[f.gen.selectedIndex].value;
   var age = f.age.value;

   if (chkw(age)){
      f.thr.value = cal_thr(age, il, gen);
   } else { 
      alert("Please enter a number for your age."); 
   }
   // Set cookies for future views of this page
   // Expires when user closes browser
   document.cookie = "thr=" + f.thr.value;
   document.cookie = "gen=" + f.gen.selectedIndex;
   document.cookie = "age=" + f.age.value;
   document.cookie = "i=" + f.il.selectedIndex;
}

function chkw(w) {
   if (isNaN(parseInt(w))) {
      return false;
   } else if (w < 0) {
      return false;
   }
   else {
      return true;
   }
}

function load_cookies() {
	var f = document.thr_input;
	f.thr.value = loadcookie("thr");
	f.gen.selectedIndex = loadcookie("gen");
	f.age.value = loadcookie("age");
	f.il.selectedIndex = loadcookie("il");
}

function loadcookie(name) {
    var allcookies = document.cookie;
	var value;
	var pos = allcookies.indexOf(name + "=");
	//alert("Name: " + name + " All: " + allcookies);
	var len = name.length + 1;  // length of name + 1
	if (pos != -1) {
		var start = pos + len;  //Start of cookie value
		var end = allcookies.indexOf(";", start);  //End of cookie value
		if (end == -1) end = allcookies.length;
		value = allcookies.substring(start,end); //Extract the value
		//alert("Name: " + name + " Value: " + value);
		value = unescape(value);  // Decode it, if encoded.
    	return value;
	}

    return 0;
}