// Parts of implementation taken from es6-shim project
  // See: https://github.com/paulmillr/es6-shim/blob/master/es6-shim.js
  
  'use strict';
  
  var expm1 = require('../expm1')
  
    , abs = Math.abs, exp = Math.exp, e = Math.E;
  
  module.exports = function (x) {
  	if (isNaN(x)) return NaN;
  	x = Number(x);
  	if (x === 0) return x;
  	if (!isFinite(x)) return x;
  	if (abs(x) < 1) return (expm1(x) - expm1(-x)) / 2;
  	return (exp(x - 1) - exp(-x - 1)) * e / 2;
  };