Implement Math.log1p using port from fdlibm.

src/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.
 
 "use strict";
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 
@@ skipping 329 matching lines @@
   } 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;
   }
 }
 
-// ES6 draft 09-27-13, section 20.2.2.20.
-// Use Taylor series to approximate. With y = x + 1;
-// log(y) at 1 == log(1) + log'(1)(y-1)/1! + log''(1)(y-1)^2/2! + ...
-//             == 0 + x - x^2/2 + x^3/3 ...
-// The closer x is to 0, the fewer terms are required.
-function MathLog1p(x) {
-  if (!IS_NUMBER(x)) x = NonNumberToNumber(x);
-  var xabs = MathAbs(x);
-  if (xabs < 1E-7) {
-    return x * (1 - x * (1/2));
-  } else if (xabs < 3E-5) {
-    return x * (1 - x * (1/2 - x * (1/3)));
-  } else if (xabs < 7E-3) {
-    return x * (1 - x * (1/2 - x * (1/3 - x * (1/4 -
-           x * (1/5 - x * (1/6 - x * (1/7)))))));
-  } else {  // Use regular log if not close enough to 0.
-    return MathLog(1 + x);
-  }
-}
-
 // -------------------------------------------------------------------
 
 function SetUpMath() {
   %CheckIsBootstrapping();
 
   %SetPrototype($Math, $Object.prototype);
   %AddNamedProperty(global, "Math", $Math, DONT_ENUM);
   %FunctionSetInstanceClassName(MathConstructor, 'Math');
 
   // Set up math constants.
@@ skipping 41 matching lines @@
     "tanh", MathTanh,
     "asinh", MathAsinh,
     "acosh", MathAcosh,
     "atanh", MathAtanh,
     "log10", MathLog10,
     "log2", MathLog2,
     "hypot", MathHypot,
     "fround", MathFroundJS,
     "clz32", MathClz32,
     "cbrt", MathCbrt,
-    "log1p", MathLog1p,
+    "log1p", MathLog1p,    // implemented by third_party/fdlibm
     "expm1", MathExpm1
   ));
 
   %SetInlineBuiltinFlag(MathCeil);
   %SetInlineBuiltinFlag(MathRandom);
   %SetInlineBuiltinFlag(MathSin);
   %SetInlineBuiltinFlag(MathCos);
 }
 
 SetUpMath();