Expose SameValue equality comparison algorithm

Since SameValue algorithm is defined formally in ECMA262 and V8 already
exported Equals and StrictEquals algorithms, SameValue should be exposed.
And in this issue, we fix the issue of Object::SameValue implementation,
SameValue(0.0, -0.0) returnes true.

BUG=v8:2909
TEST=cctest/test-api/Equality
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/24360017

Patch from Yusuke Suzuki <yusukesuzuki@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16924 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -1479,6 +1479,7 @@ class V8_EXPORT Value : public Data {
   /** JS == */
   bool Equals(Handle<Value> that) const;
   bool StrictEquals(Handle<Value> that) const;
+  bool SameValue(Handle<Value> that) const;
 
   template <class T> V8_INLINE static Value* Cast(T* value);
 

src/api.cc

@@ -3055,6 +3055,19 @@ bool Value::StrictEquals(Handle<Value> that) const {
 }
 
 
+bool Value::SameValue(Handle<Value> that) const {
+  i::Isolate* isolate = i::Isolate::Current();
+  if (EmptyCheck("v8::Value::SameValue()", this) ||
+      EmptyCheck("v8::Value::SameValue()", that)) {
+    return false;
+  }
+  LOG_API(isolate, "SameValue");
+  i::Handle<i::Object> obj = Utils::OpenHandle(this);
+  i::Handle<i::Object> other = Utils::OpenHandle(*that);
+  return obj->SameValue(*other);
+}
+
+
 uint32_t Value::Uint32Value() const {
   i::Handle<i::Object> obj = Utils::OpenHandle(this);
   if (obj->IsSmi()) {

src/objects.cc

@@ -1005,8 +1005,11 @@ bool Object::SameValue(Object* other) {
   if (IsNumber() && other->IsNumber()) {
     double this_value = Number();
     double other_value = other->Number();
-    return (this_value == other_value) ||
-        (std::isnan(this_value) && std::isnan(other_value));
+    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));
   }
   if (IsString() && other->IsString()) {
     return String::cast(this)->Equals(String::cast(other));

test/cctest/test-api.cc

@@ -4973,7 +4973,7 @@ THREADED_TEST(Equality) {
   CHECK(!v8_str("5")->StrictEquals(v8_num(5)));
   CHECK(v8_num(1)->StrictEquals(v8_num(1)));
   CHECK(!v8_num(1)->StrictEquals(v8_num(2)));
-  CHECK(v8_num(0)->StrictEquals(v8_num(-0)));
+  CHECK(v8_num(0.0)->StrictEquals(v8_num(-0.0)));
   Local<Value> not_a_number = v8_num(i::OS::nan_value());
   CHECK(!not_a_number->StrictEquals(not_a_number));
   CHECK(v8::False()->StrictEquals(v8::False()));
@@ -4983,6 +4983,16 @@ THREADED_TEST(Equality) {
   v8::Persistent<v8::Object> alias(isolate, obj);
   CHECK(v8::Local<v8::Object>::New(isolate, alias)->StrictEquals(obj));
   alias.Dispose();
+
+  CHECK(v8_str("a")->SameValue(v8_str("a")));
+  CHECK(!v8_str("a")->SameValue(v8_str("b")));
+  CHECK(!v8_str("5")->SameValue(v8_num(5)));
+  CHECK(v8_num(1)->SameValue(v8_num(1)));
+  CHECK(!v8_num(1)->SameValue(v8_num(2)));
+  CHECK(!v8_num(0.0)->SameValue(v8_num(-0.0)));
+  CHECK(not_a_number->SameValue(not_a_number));
+  CHECK(v8::False()->SameValue(v8::False()));
+  CHECK(!v8::False()->SameValue(v8::Undefined()));
 }