update hash code logic on the web

lib/web_ui/lib/src/ui/hash_codes.dart

@@ -4,102 +4,90 @@
 
 part of ui;
 
-class _HashEnd {
-  const _HashEnd();
-}
-
+class _HashEnd { const _HashEnd(); }
 const _HashEnd _hashEnd = _HashEnd();
 
-/// Combine up to twenty values' hashCodes into one value.
+/// Jenkins hash function, optimized for small integers.
+//
+// Borrowed from the dart sdk: sdk/lib/math/jenkins_smi_hash.dart.
+class _Jenkins {
+  static int combine(int hash, Object o) {
+    assert(o is! Iterable);
+    hash = 0x1fffffff & (hash + o.hashCode);
+    hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
+    hash = hash ^ (hash >> 6);
+    return hash;
+  }
+
+  static int finish(int hash) {
+    hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
+    hash = hash ^ (hash >> 11);
+    hash = 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
+    return hash;
+  }
+}
+
+/// Combine up to twenty objects' hash codes into one value.
 ///
-/// If you only need to handle one value's hashCode, then just refer to its
-/// [hashCode] getter directly.
+/// If you only need to handle one object's hash code, then just refer to its
+/// [Object.hashCode] getter directly.
 ///
-/// If you need to combine an arbitrary number of values from a List or other
-/// Iterable, use [hashList]. The output of hashList can be used as one of the
-/// arguments to this function.
+/// If you need to combine an arbitrary number of objects from a [List] or other
+/// [Iterable], use [hashList]. The output of [hashList] can be used as one of
+/// the arguments to this function.
 ///
 /// For example:
 ///
-///   int hashCode => hashValues(foo, bar, hashList(quux), baz);
-int hashValues(Object arg01, Object arg02,
-    [Object arg03 = _hashEnd,
-    Object arg04 = _hashEnd,
-    Object arg05 = _hashEnd,
-    Object arg06 = _hashEnd,
-    Object arg07 = _hashEnd,
-    Object arg08 = _hashEnd,
-    Object arg09 = _hashEnd,
-    Object arg10 = _hashEnd,
-    Object arg11 = _hashEnd,
-    Object arg12 = _hashEnd,
-    Object arg13 = _hashEnd,
-    Object arg14 = _hashEnd,
-    Object arg15 = _hashEnd,
-    Object arg16 = _hashEnd,
-    Object arg17 = _hashEnd,
-    Object arg18 = _hashEnd,
-    Object arg19 = _hashEnd,
-    Object arg20 = _hashEnd]) {
-  int result = 373;
-  assert(arg01 is! Iterable);
-  result = 37 * result + arg01.hashCode;
-  assert(arg02 is! Iterable);
-  result = 37 * result + arg02.hashCode;
+/// ```dart
+/// int hashCode => hashValues(foo, bar, hashList(quux), baz);
+/// ```
+int hashValues(
+  Object arg01,            Object arg02,          [ Object arg03 = _hashEnd,
+  Object arg04 = _hashEnd, Object arg05 = _hashEnd, Object arg06 = _hashEnd,
+  Object arg07 = _hashEnd, Object arg08 = _hashEnd, Object arg09 = _hashEnd,
+  Object arg10 = _hashEnd, Object arg11 = _hashEnd, Object arg12 = _hashEnd,
+  Object arg13 = _hashEnd, Object arg14 = _hashEnd, Object arg15 = _hashEnd,
+  Object arg16 = _hashEnd, Object arg17 = _hashEnd, Object arg18 = _hashEnd,
+  Object arg19 = _hashEnd, Object arg20 = _hashEnd ]) {
+  int result = 0;
+  result = _Jenkins.combine(result, arg01);
+  result = _Jenkins.combine(result, arg02);
   if (arg03 != _hashEnd) {
-    assert(arg03 is! Iterable);
-    result = 37 * result + arg03.hashCode;
+    result = _Jenkins.combine(result, arg03);
     if (arg04 != _hashEnd) {
-      assert(arg04 is! Iterable);
-      result = 37 * result + arg04.hashCode;
+      result = _Jenkins.combine(result, arg04);
       if (arg05 != _hashEnd) {
-        assert(arg05 is! Iterable);
-        result = 37 * result + arg05.hashCode;
+        result = _Jenkins.combine(result, arg05);
         if (arg06 != _hashEnd) {
-          assert(arg06 is! Iterable);
-          result = 37 * result + arg06.hashCode;
+          result = _Jenkins.combine(result, arg06);
           if (arg07 != _hashEnd) {
-            assert(arg07 is! Iterable);
-            result = 37 * result + arg07.hashCode;
+            result = _Jenkins.combine(result, arg07);
             if (arg08 != _hashEnd) {
-              assert(arg08 is! Iterable);
-              result = 37 * result + arg08.hashCode;
+              result = _Jenkins.combine(result, arg08);
               if (arg09 != _hashEnd) {
-                assert(arg09 is! Iterable);
-                result = 37 * result + arg09.hashCode;
+                result = _Jenkins.combine(result, arg09);
                 if (arg10 != _hashEnd) {
-                  assert(arg10 is! Iterable);
-                  result = 37 * result + arg10.hashCode;
+                  result = _Jenkins.combine(result, arg10);
                   if (arg11 != _hashEnd) {
-                    assert(arg11 is! Iterable);
-                    result = 37 * result + arg11.hashCode;
+                    result = _Jenkins.combine(result, arg11);
                     if (arg12 != _hashEnd) {
-                      assert(arg12 is! Iterable);
-                      result = 37 * result + arg12.hashCode;
+                      result = _Jenkins.combine(result, arg12);
                       if (arg13 != _hashEnd) {
-                        assert(arg13 is! Iterable);
-                        result = 37 * result + arg13.hashCode;
+                        result = _Jenkins.combine(result, arg13);
                         if (arg14 != _hashEnd) {
-                          assert(arg14 is! Iterable);
-                          result = 37 * result + arg14.hashCode;
+                          result = _Jenkins.combine(result, arg14);
                           if (arg15 != _hashEnd) {
-                            assert(arg15 is! Iterable);
-                            result = 37 * result + arg15.hashCode;
+                            result = _Jenkins.combine(result, arg15);
                             if (arg16 != _hashEnd) {
-                              assert(arg16 is! Iterable);
-                              result = 37 * result + arg16.hashCode;
+                              result = _Jenkins.combine(result, arg16);
                               if (arg17 != _hashEnd) {
-                                assert(arg17 is! Iterable);
-                                result = 37 * result + arg17.hashCode;
+                                result = _Jenkins.combine(result, arg17);
                                 if (arg18 != _hashEnd) {
-                                  assert(arg18 is! Iterable);
-                                  result = 37 * result + arg18.hashCode;
+                                  result = _Jenkins.combine(result, arg18);
                                   if (arg19 != _hashEnd) {
-                                    assert(arg19 is! Iterable);
-                                    result = 37 * result + arg19.hashCode;
+                                    result = _Jenkins.combine(result, arg19);
                                     if (arg20 != _hashEnd) {
-                                      assert(arg20 is! Iterable);
-                                      result = 37 * result + arg20.hashCode;
+                                      result = _Jenkins.combine(result, arg20);
                                       // I can see my house from here!
                                     }
                                   }
@@ -119,19 +107,17 @@ int hashValues(Object arg01, Object arg02,
       }
     }
   }
-  return result;
+  return _Jenkins.finish(result);
 }
 
-/// Combine the hashCodes of an arbitrary number of values from an Iterable into
-/// one value. This function will return the same value if given "null" as if
-/// given an empty list.
-int hashList(Iterable<Object> args) {
-  int result = 373;
-  if (args != null) {
-    for (Object arg in args) {
-      assert(arg is! Iterable);
-      result = 37 * result + arg.hashCode;
-    }
+/// Combine the [Object.hashCode] values of an arbitrary number of objects from
+/// an [Iterable] into one value. This function will return the same value if
+/// given null as if given an empty list.
+int hashList(Iterable<Object> arguments) {
+  int result = 0;
+  if (arguments != null) {
+    for (Object argument in arguments)
+      result = _Jenkins.combine(result, argument);
   }
-  return result;
+  return _Jenkins.finish(result);
 }

lib/web_ui/test/hash_codes_test.dart

@@ -0,0 +1,122 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:test/test.dart';
+import 'package:ui/ui.dart';
+
+// The biggest integer value that can be represented in JavaScript is 1 << 53.
+// However, the 1 << 53 expression cannot be used in JavaScript because that
+// would apply the bitwise shift to a "number" (i.e. float64), which is
+// meaningless. Instead, a decimal literal is used here.
+const int _kBiggestExactJavaScriptInt = 9007199254740992;
+
+void main() {
+  test('hashValues can hash lots of huge values effectively', () {
+    expect(
+      hashValues(
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+      ),
+      496984395,
+    );
+    // Hash a slightly smaller number to verify that the hash code is different.
+    expect(
+      hashValues(
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt - 1,
+      ),
+      455584273,
+    );
+  });
+
+  test('hashList can hash lots of huge values effectively', () {
+    expect(
+      hashList(<int>[
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+      ]),
+      496984395,
+    );
+    // Hash a slightly smaller number to verify that the hash code is different.
+    expect(
+      hashList(<int>[
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt,
+        _kBiggestExactJavaScriptInt - 1,
+      ]),
+      455584273,
+    );
+  });
+}