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

runtime/lib/math.cc

 // Copyright (c) 2011, 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.
 
 #include <ctype.h>  // isspace.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/exceptions.h"
@@ skipping 48 matching lines @@
 DEFINE_NATIVE_ENTRY(Math_exp, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(Double, operand, arguments->NativeArgAt(0));
   return Double::New(exp(operand.value()));
 }
 
 DEFINE_NATIVE_ENTRY(Math_log, 1) {
   GET_NON_NULL_NATIVE_ARGUMENT(Double, operand, arguments->NativeArgAt(0));
   return Double::New(log(operand.value()));
 }
 
+
+// Returns the typed-data array store in '_Random._state' field.
+static RawTypedData* GetRandomStateArray(const Instance& receiver) {
+  const Class& random_class = Class::Handle(receiver.clazz());
+  const Field& state_field =
+      Field::Handle(random_class.LookupField(Symbols::_state()));
+  ASSERT(!state_field.IsNull());
+  const Instance& state_field_value =
+      Instance::Cast(Object::Handle(receiver.GetField(state_field)));

[siva, 2013/08/02 22:46:13]

Why cast this to an Instance, it is being cast to TypedData below
why not just retain it as an Object:

const Object& state_field_value = Object::Handle(...);

+  ASSERT(!state_field_value.IsNull());
+  ASSERT(state_field_value.IsTypedData());
+  const TypedData& array = TypedData::Cast(state_field_value);
+  ASSERT(array.Length() == 2);
+  ASSERT(array.ElementType() == kUint32ArrayElement);
+  return array.raw();
+}
+
+
+// Implements:
+//   var state = ((_A * (_state[kSTATE_LO])) + _state[kSTATE_HI]) & _MASK_64;
+//   _state[kSTATE_LO] = state & _MASK_32;
+//   _state[kSTATE_HI] = state >> 32;
+DEFINE_NATIVE_ENTRY(Random_nextState, 1) {
+  GET_NON_NULL_NATIVE_ARGUMENT(Instance, receiver, arguments->NativeArgAt(0));
+  const TypedData& array = TypedData::Handle(GetRandomStateArray(receiver));
+  const uint64_t state_lo = array.GetUint32(0);
+  const uint64_t state_hi = array.GetUint32(array.ElementSizeInBytes());

[siva, 2013/08/02 22:46:13]

might be more readable to have:
const intptr_t state_lo_offset = 0;
const intptr_t state_hi_offset = 1 * array.ElementSizeInBytes();
and use these in GetUint32(...) and SetUint32(...)

+  const uint64_t A = 0xffffda61;
+  uint64_t state = (A * state_lo) + state_hi;
+  array.SetUint32(0, static_cast<uint32_t>(state));
+  array.SetUint32(array.ElementSizeInBytes(),
+      static_cast<uint32_t>(state >> 32));
+  return Object::null();
+}
+
+
+// Implements:
+//   do {
+//     seed = (seed + 0x5A17) & _Random._MASK_64;
+//   } while (seed == 0);
+//   _state[kSTATE_LO] = seed & _MASK_32;
+//   _state[kSTATE_HI] = seed >> 32;
+DEFINE_NATIVE_ENTRY(Random_setupSeed, 2) {
+  GET_NON_NULL_NATIVE_ARGUMENT(Instance, receiver, arguments->NativeArgAt(0));
+  GET_NON_NULL_NATIVE_ARGUMENT(Integer, seed_int, arguments->NativeArgAt(1));
+  const TypedData& array = TypedData::Handle(GetRandomStateArray(receiver));
+  ASSERT(!seed_int.IsNull());
+  ASSERT(!array.IsNull());
+  // TODO(srdjan): Reduce Bigint to 64 bit value.
+  int64_t seed = seed_int.IsBigint() ? 0 : seed_int.AsInt64Value();
+  do {
+    seed = seed + 0x5A17;
+  } while (seed == 0);
+  array.SetUint32(0, static_cast<uint32_t>(seed));
+  array.SetUint32(array.ElementSizeInBytes(),

[siva, 2013/08/02 22:46:13]

Ditto comment about offsets.

+      static_cast<uint32_t>(seed >> 32));
+  return Object::null();
+}
+
 }  // namespace dart