| // 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/dart.h" |
| #include "vm/flags.h" |
| #include "vm/os.h" |
| |
| namespace dart { |
| |
| DEFINE_FLAG(uint64_t, |
| random_seed, |
| 0, |
| "Override the random seed for debugging."); |
| |
| Random::Random() { |
| uint64_t seed = FLAG_random_seed; |
| if (seed == 0) { |
| Dart_EntropySource callback = Dart::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(); |
| } |
| Initialize(seed); |
| } |
| |
| void Random::Initialize(uint64_t seed) { |
| ASSERT(seed != 0); |
| // Crank the next state a couple of times. |
| _state = seed; |
| NextState(); |
| NextState(); |
| NextState(); |
| NextState(); |
| } |
| |
| Random::Random(uint64_t seed) { |
| Initialize(seed); |
| } |
| |
| 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 |