Implement Math.expm1 using port from fdlibm.

src/math.js

Index: src/math.js
diff --git a/src/math.js b/src/math.js
index 13cdb31cdcf5ec0b58a24d4ad9daf1f10b5561bf..00a507a28e5514d0ebdfcb81acc194821e443a98 100644
--- a/src/math.js
+++ b/src/math.js
@@ -327,26 +327,6 @@ function CubeRoot(x) {
   return NEWTON_ITERATION_CBRT(x, approx);
 }
 
-// ES6 draft 09-27-13, section 20.2.2.14.
-// Use Taylor series to approximate.
-// exp(x) - 1 at 0 == -1 + exp(0) + exp'(0)*x/1! + exp''(0)*x^2/2! + ...
-//                 == x/1! + x^2/2! + x^3/3! + ...
-// The closer x is to 0, the fewer terms are required.
-function MathExpm1(x) {
-  if (!IS_NUMBER(x)) x = NonNumberToNumber(x);
-  var xabs = MathAbs(x);
-  if (xabs < 2E-7) {
-    return x * (1 + x * (1/2));
-  } else if (xabs < 6E-5) {
-    return x * (1 + x * (1/2 + x * (1/6)));
-  } else if (xabs < 2E-2) {
-    return x * (1 + x * (1/2 + x * (1/6 +
-           x * (1/24 + x * (1/120 + x * (1/720))))));
-  } else {  // Use regular exp if not close enough to 0.
-    return MathExp(x) - 1;
-  }
-}
-
 // -------------------------------------------------------------------
 
 function SetUpMath() {
@@ -408,8 +388,8 @@ function SetUpMath() {
     "fround", MathFroundJS,
     "clz32", MathClz32,
     "cbrt", MathCbrt,
-    "log1p", MathLog1p,    // implemented by third_party/fdlibm
-    "expm1", MathExpm1
+    "log1p", MathLog1p,   // implemented by third_party/fdlibm
+    "expm1", MathExpm1    // implemented by third_party/fdlibm
   ));
 
   %SetInlineBuiltinFlag(MathCeil);