Implement Math.tanh using fdlibm port.

src/js/math.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var rngstate;  // Initialized to a Uint32Array during genesis.
 
 (function(global, utils) {
 "use strict";
 
 %CheckIsBootstrapping();
@@ skipping 164 matching lines @@
 
 // ES6 draft 09-27-13, section 20.2.2.34.
 function MathTrunc(x) {
   x = +x;
   if (x > 0) return %_MathFloor(x);
   if (x < 0) return -%_MathFloor(-x);
   // -0, 0 or NaN.
   return x;
 }
 
-// ES6 draft 09-27-13, section 20.2.2.33.
-function MathTanh(x) {
-  x = TO_NUMBER(x);
-  // Idempotent for +/-0.
-  if (x === 0) return x;
-  // Returns +/-1 for +/-Infinity.
-  if (!NUMBER_IS_FINITE(x)) return MathSign(x);
-  var exp1 = MathExp(x);
-  var exp2 = MathExp(-x);
-  return (exp1 - exp2) / (exp1 + exp2);
-}
-
 // ES6 draft 09-27-13, section 20.2.2.5.
 function MathAsinh(x) {
   x = TO_NUMBER(x);
   // Idempotent for NaN, +/-0 and +/-Infinity.
   if (x === 0 || !NUMBER_IS_FINITE(x)) return x;
   if (x > 0) return MathLog(x + %_MathSqrt(x * x + 1));
   // This is to prevent numerical errors caused by large negative x.
   return -MathLog(-x + %_MathSqrt(x * x + 1));
 }
 
@@ skipping 115 matching lines @@
   "log", MathLog,
   "round", MathRound,
   "sqrt", MathSqrtJS,
   "atan2", MathAtan2JS,
   "pow", MathPowJS,
   "max", MathMax,
   "min", MathMin,
   "imul", MathImul,
   "sign", MathSign,
   "trunc", MathTrunc,
-  "tanh", MathTanh,
   "asinh", MathAsinh,
   "acosh", MathAcosh,
   "atanh", MathAtanh,
   "hypot", MathHypot,
   "fround", MathFroundJS,
   "clz32", MathClz32JS,
   "cbrt", MathCbrt
 ]);
 
 %SetForceInlineFlag(MathAbs);
@@ skipping 15 matching lines @@
 utils.Export(function(to) {
   to.MathAbs = MathAbs;
   to.MathExp = MathExp;
   to.MathFloor = MathFloorJS;
   to.IntRandom = MathRandomRaw;
   to.MathMax = MathMax;
   to.MathMin = MathMin;
 });
 
 })