Improve _toInt64() and _toUint64() conversions in TypedData.

runtime/lib/typed_data.dart

Index: runtime/lib/typed_data.dart
===================================================================
--- runtime/lib/typed_data.dart	(revision 43696)
+++ runtime/lib/typed_data.dart	(working copy)
@@ -3588,12 +3588,22 @@
 
 
 int _toInt64(int value) {
-  return _toInt(value, 0xFFFFFFFFFFFFFFFF);  // TODO(regis): Avoid bigint mask.
+  // Avoid bigint mask when possible.
+  var cid = ClassID.getID(value);
+  if (cid == ClassID.cidSmi || cid == ClassID.cidMint) {

[srdjan, 2015/02/11 20:40:06]

Please add parentheses.
Maybe instead of two tests you could only do:

return (cid == ClassID.cidBigint) ? _toInt(value, 0xFFFFFFFFFFFFFFFF) : value;

[regis, 2015/02/11 20:51:17]

Done.

+    return value;
+  }
+  return _toInt(value, 0xFFFFFFFFFFFFFFFF);
 }
 
 
 int _toUint64(int value) {
-  return value & 0xFFFFFFFFFFFFFFFF;  // TODO(regis): Avoid bigint mask.
+  // Avoid bigint mask when possible.
+  var cid = ClassID.getID(value);
+  if (cid == ClassID.cidSmi || cid == ClassID.cidMint) {

[srdjan, 2015/02/11 20:40:06]

ditto

[regis, 2015/02/11 20:51:17]

Done.

+    return value;
+  }
+  return _toInt(value, 0xFFFFFFFFFFFFFFFF);
 }