Adapt Random class to be able to run in javascript integer compatibility mode.

runtime/lib/math_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:typed_data";
 
 // A VM patch of the dart:math library.
 
 // If [x] is an [int] and [exponent] is a non-negative [int], the result is
 // an [int], otherwise the result is a [double].
@@ skipping 28 matching lines @@
 double _log(double x) native "Math_log";
 
 
 // TODO(iposva): Handle patch methods within a patch class correctly.
 patch class Random {
 
   /*patch*/ factory Random([int seed]) {
     if (seed == null) {
       seed = _Random._nextSeed();
     }
-    do {
-      seed = (seed + 0x5A17) & _Random._MASK_64;
-    } while (seed == 0);
     // Crank a couple of times to distribute the seed bits a bit further.
-    return new _Random._internal(seed).._nextState()
-                                      .._nextState()
-                                      .._nextState()
-                                      .._nextState();
+    return new _Random().._setupSeed(seed)
+                        .._nextState()
+                        .._nextState()
+                        .._nextState()
+                        .._nextState();
   }
 }
 
 
 class _Random implements Random {
   // Internal state of the random number generator.
   final _state = new Uint32List(2);
   static const kSTATE_LO = 0;
   static const kSTATE_HI = 1;
 
-  _Random._internal(state) {
-    _state[kSTATE_LO] = state & _MASK_32;
-    _state[kSTATE_HI] = state >> 32;
-  }
+  // Implements:
+  //   do {
+  //     seed = (seed + 0x5A17) & _Random._MASK_64;
+  //   } while (seed == 0);
+  //   _state[kSTATE_LO] = seed & _MASK_32;
+  //   _state[kSTATE_HI] = seed >> 32;
+  // This is a native to prevent 64-bit operations in Dart, which
+  // fail with --throw_on_javascript_int_overflow.
+  void _setupSeed(int seed) native "Random_setupSeed";
 
   // The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32.
   // http://en.wikipedia.org/wiki/Multiply-with-carry
   // The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1.
-  void _nextState() {
-    var state = ((_A * (_state[kSTATE_LO])) + _state[kSTATE_HI]) & _MASK_64;
-    _state[kSTATE_LO] = state & _MASK_32;
-    _state[kSTATE_HI] = state >> 32;
-  }
+
+  // Implements:
+  //   var state = ((_A * (_state[kSTATE_LO])) + _state[kSTATE_HI]) & _MASK_64;
+  //   _state[kSTATE_LO] = state & _MASK_32;
+  //   _state[kSTATE_HI] = state >> 32;
+  // This is a native to prevent 64-bit operations in Dart, which
+  // fail with --throw_on_javascript_int_overflow.
+  void _nextState() native "Random_nextState";
 
   int nextInt(int max) {
     // TODO(srdjan): Remove the 'limit' check once optimizing  comparison of
     // Smi-s with Mint constants.
     final limit = 0x3FFFFFFF;
     if (max <= 0 || ((max > limit) && (max > _POW2_32))) {
       throw new ArgumentError("max must be positive and < 2^32:"
                                          " $max");
     }
     if ((max & -max) == max) {
       // Fast case for powers of two.
       _nextState();
       return _state[kSTATE_LO] & (max - 1);
     }
 
     var rnd32;
     var result;
     do {
       _nextState();
       rnd32 = _state[kSTATE_LO];
       result = rnd32 % max;
     } while ((rnd32 - result + max) >= _POW2_32);
     return result;
   }
 
   double nextDouble() {
-    return ((nextInt(1 << 26) << 27) + nextInt(1 << 27)) / _POW2_53_D;
+    return ((nextInt(1 << 26) * _POW2_27_D) + nextInt(1 << 27)) / _POW2_53_D;
   }
 
   bool nextBool() {
     return nextInt(2) == 0;
   }
 
   // Constants used by the algorithm or masking.
   static const _MASK_32 = (1 << 32) - 1;
   static const _MASK_64 = (1 << 64) - 1;
   static const _POW2_32 = 1 << 32;
   static const _POW2_53_D = 1.0 * (1 << 53);
+  static const _POW2_27_D = 1.0 * (1 << 27);
 
   static const _A = 0xffffda61;
 
   // Use a singleton Random object to get a new seed if no seed was passed.
   static var _prng = null;
 
   static int _nextSeed() {
     if (_prng == null) {
       // TODO(iposva): Use system to get a random seed.
       _prng = new Random(new DateTime.now().millisecondsSinceEpoch);
     }
     // Trigger the PRNG once to change the internal state.
     _prng._nextState();
     return _prng._state[kSTATE_LO];
   }
 }