function _log2Complex(x) {
    var newX = Math.sqrt(x.re * x.re + x.im * x.im);
    return new type.Complex(Math.log2 ? Math.log2(newX) : Math.log(newX) / Math.LN2, Math.atan2(x.im, x.re) / Math.LN2);
  }
Calculate log2 for a complex value
@param {Complex} x
@returns {Complex}
@private