export default function(pp, arg_r) {
  var r = 2 * Math.cos(arg_r);
  var i = pp.length - 1;
  var hr1 = pp[i];
  var hr2 = 0;
  var hr;

  while (--i >= 0) {
    hr = -hr2 + r * hr1 + pp[i];
    hr2 = hr1;
    hr1 = hr;
  }

  return Math.sin(arg_r) * hr;
}