--- /dev/null
+// 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;
+};