Implement String.hashCode.

dart/frog/leg/lib/js_helper.dart

Index: dart/frog/leg/lib/js_helper.dart
diff --git a/dart/frog/leg/lib/js_helper.dart b/dart/frog/leg/lib/js_helper.dart
index d730fa097f52c06284dd16c8f6629a26c3af305f..86c85b539a8636b8d82a8a9e672226c357e180ab 100644
--- a/dart/frog/leg/lib/js_helper.dart
+++ b/dart/frog/leg/lib/js_helper.dart
@@ -359,7 +359,7 @@ builtin$charCodeAt$1(var receiver, int index) {
     if (index is !num) throw new IllegalArgumentException(index);
     if (index < 0) throw new IndexOutOfRangeException(index);
     if (index >= receiver.length) throw new IndexOutOfRangeException(index);
-    return JS("string", @"$0.charCodeAt($1)", receiver, index);
+    return JS("int", @"$0.charCodeAt($1)", receiver, index);
   } else {
     return UNINTERCEPTED(receiver.charCodeAt(index));
   }
@@ -1180,15 +1180,27 @@ class MathNatives {
   static double random() => JS("double", @"Math.random()");
 }
 
+/**
+ * This is the [Jenkins hash function][1], but always using XOR
+ * instead of addition to keep the hash value in 32bit. This was
+ * inspired by jmesserly's work in Frog. However, using XOR is 40%
+ * faster than the original version in Frog.
+ *
+ * [1]: http://en.wikipedia.org/wiki/Jenkins_hash_function
+ */
 builtin$hashCode$0(receiver) {
-  if (receiver is num) return receiver & 0x1FFFFFFF;
-  if (receiver is String) {
-    throw 'String.hashCode is not implemented';
-  }
-  if (isJsArray(receiver)) {
-    throw 'List.hashCode is not implemented';
-  }
-  return UNINTERCEPTED(receiver.hashCode());
+  if (receiver is num) return JS('int', @'$0 & 0x1FFFFFFF', receiver);

[ngeoffray, 2012/02/28 10:13:25]

Please add a TODO to make sure we change the code to the original once our
optimizations are smarter.

[ahe, 2012/02/28 17:26:10]

Done.

+  if (receiver is !String) return UNINTERCEPTED(receiver.hashCode());
+  int hash = 0;
+  int length = JS('int', @'$0.length', receiver);
+  for (int i = 0; i < length; i++) {
+    hash ^= JS('int', @'$0.charCodeAt($1)', receiver, i);
+    hash ^= JS("int", @"$0 << $1", hash, 10);
+    hash ^= hash >> 6;
+  }
+  hash ^= JS("int", @"$0 << $1", hash, 3);
+  hash ^= hash >> 11;
+  return 0x1fffffff & (hash ^ JS("int", @"$0 << $1", hash, 15));
 }
 
 // TODO(ahe): Dynamic may be overridden.