V8: Add utility functions to check SameValue and SameValueZero.

Adds SameValue and SameValueZero functions for float and double.
These will be used for HeapNumber and SIMD values.

LOG=N
BUG=v8:4124

Review URL: https://codereview.chromium.org/1234073003

Cr-Commit-Position: refs/heads/master@{#29660}

src/objects.cc

@@ -683,13 +683,7 @@ bool Object::SameValue(Object* other) {
   // The object is either a number, a name, an odd-ball,
   // a real JS object, or a Harmony proxy.
   if (IsNumber() && other->IsNumber()) {
-    double this_value = Number();
-    double other_value = other->Number();
-    bool equal = this_value == other_value;
-    // SameValue(NaN, NaN) is true.
-    if (!equal) return std::isnan(this_value) && std::isnan(other_value);
-    // SameValue(0.0, -0.0) is false.
-    return (this_value != 0) || ((1 / this_value) == (1 / other_value));
+    return v8::internal::SameValue(Number(), other->Number());
   }
   if (IsString() && other->IsString()) {
     return String::cast(this)->Equals(String::cast(other));
@@ -704,11 +698,7 @@ bool Object::SameValueZero(Object* other) {
   // The object is either a number, a name, an odd-ball,
   // a real JS object, or a Harmony proxy.
   if (IsNumber() && other->IsNumber()) {
-    double this_value = Number();
-    double other_value = other->Number();
-    // +0 == -0 is true
-    return this_value == other_value
-        || (std::isnan(this_value) && std::isnan(other_value));
+    return v8::internal::SameValueZero(Number(), other->Number());
   }
   if (IsString() && other->IsString()) {
     return String::cast(this)->Equals(String::cast(other));

src/utils.h

@@ -200,6 +200,27 @@ inline double Floor(double x) {
   return std::floor(x);
 }
 
+// Implements the ES5 SameValue operation for floating point types.
+// http://www.ecma-international.org/ecma-262/6.0/#sec-samevalue
+template <typename T>
+bool SameValue(T x, T y) {
+  // SameValue(NaN, NaN) is true.
+  if (x != y) return std::isnan(x) && std::isnan(y);
+  // SameValue(0, -0) is false.
+  if (std::signbit(x) != std::signbit(y)) return false;
+  return true;
+}
+
+
+// Implements the ES6 SameValueZero operation for floating point types.
+// http://www.ecma-international.org/ecma-262/6.0/#sec-samevaluezero
+template <typename T>
+bool SameValueZero(T x, T y) {
+  if (x != y) return std::isnan(x) && std::isnan(y);
+  // SameValueZero doesn't distinguish between 0 and -0.
+  return true;
+}
+
 
 // TODO(svenpanne) Clean up the whole power-of-2 mess.
 inline int32_t WhichPowerOf2Abs(int32_t x) {