'use strict';
  
  var log = Math.log, LOG2E = Math.LOG2E;
  
  module.exports = function (x) {
  	if (isNaN(x)) return NaN;
  	x = Number(x);
  	if (x < 0) return NaN;
  	if (x === 0) return -Infinity;
  	if (x === 1) return 0;
  	if (x === Infinity) return Infinity;
  
  	return log(x) * LOG2E;
  };