Fix issue with -0 in Maps

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 100cbf90b3493860d8bd0c5c5b4246d8f57e495d..99b0ab70de998065185c0d504ba487f31b6a08a7 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -798,10 +798,16 @@ Map* Object::GetRootMap(Isolate* isolate) {
 Object* Object::GetHash() {
   // The object is either a number, a name, an odd-ball,
   // a real JS object, or a Harmony proxy.
-  if (IsNumber()) {
-    uint32_t hash = std::isnan(Number())
-                        ? Smi::kMaxValue
-                        : ComputeLongHash(double_to_uint64(Number()));
+  if (IsSmi()) {

[arv (Not doing code reviews), 2015/02/20 19:19:08]

IsNumber() checked IsSmi() || IsHeapNumber()

If it is a Smi it cannot be a NaN or -0.

+    int num = Smi::cast(this)->value();
+    uint32_t hash = ComputeLongHash(double_to_uint64(static_cast<double>(num)));

[arv (Not doing code reviews), 2015/02/20 19:19:08]

I tried a few other approaches here but it is important that we compute the same
hash code here as in the heap number case.

[adamk, 2015/02/20 19:50:03]

This is fine for now, and the right approach for this patch (changing only one
thing at a time) but soon I'll be creating a patch to use a 32-bit hash function
for Smis, and have code in the IsHeapNumber branch to compute the same 32-bit
hash for Smi-representable doubles.

+    return Smi::FromInt(hash & Smi::kMaxValue);
+  }
+  if (IsHeapNumber()) {
+    double num = HeapNumber::cast(this)->value();
+    if (std::isnan(num)) return Smi::FromInt(Smi::kMaxValue);
+    if (i::IsMinusZero(num)) num = 0;

[adamk, 2015/02/20 19:50:03]

Nit: shouldn't need the "i::" prefix here.

[arv (Not doing code reviews), 2015/02/20 20:05:34]

It is needed. There is a class function with the same name.

+    uint32_t hash = ComputeLongHash(double_to_uint64(num));
     return Smi::FromInt(hash & Smi::kMaxValue);
   }
   if (IsName()) {