- Add a per-isolate pseudo random number generator to the

runtime/vm/random.cc

+// Copyright (c) 2013, 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 "vm/random.h"
+#include "vm/flags.h"
+#include "vm/isolate.h"
+
+namespace dart {
+
+DEFINE_FLAG(int, random_seed, 0, "Override the random seed for debugging.");
+
+Random::Random() {
+  uint64_t seed = FLAG_random_seed;
+  if (seed == 0) {
+    Dart_EntropySource callback = Isolate::entropy_source_callback();
+    if (callback != NULL) {
+      if (!callback(reinterpret_cast<uint8_t*>(&seed), sizeof(seed))) {
+        // Callback failed. Reset the seed to 0.
+        seed = 0;
+      }
+    }
+  }
+  if (seed == 0) {
+    // We did not get a seed so far. As a fallback we do use the current time.
+    seed = OS::GetCurrentTimeMicros();
+  }
+  // Crank the next state a couple of times.
+  _state = seed;
+  NextState();
+  NextState();
+  NextState();
+  NextState();
+}
+
+Random::~Random() {
+  // Nothing to be done here.
+}
+
+// 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 Random::NextState() {
+  const uint64_t MASK_32 = 0xffffffff;
+  const uint64_t A = 0xffffda61;
+
+  uint64_t state_lo = _state & MASK_32;
+  uint64_t state_hi = (_state >> 32) & MASK_32;
+  _state = (A * state_lo) + state_hi;
+}
+
+
+uint32_t Random::NextUInt32() {
+  const uint64_t MASK_32 = 0xffffffff;
+  NextState();
+  return static_cast<uint32_t>(_state & MASK_32);
+}
+
+}  // namespace dart