OLD | NEW |
(Empty) | |
| 1 // Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file |
| 2 // for details. All rights reserved. Use of this source code is governed by a |
| 3 // BSD-style license that can be found in the LICENSE file. |
| 4 |
| 5 #include "vm/random.h" |
| 6 #include "vm/flags.h" |
| 7 #include "vm/isolate.h" |
| 8 |
| 9 namespace dart { |
| 10 |
| 11 DEFINE_FLAG(int, random_seed, 0, "Override the random seed for debugging."); |
| 12 |
| 13 Random::Random() { |
| 14 uint64_t seed = FLAG_random_seed; |
| 15 if (seed == 0) { |
| 16 Dart_EntropySource callback = Isolate::entropy_source_callback(); |
| 17 if (callback != NULL) { |
| 18 if (!callback(reinterpret_cast<uint8_t*>(&seed), sizeof(seed))) { |
| 19 // Callback failed. Reset the seed to 0. |
| 20 seed = 0; |
| 21 } |
| 22 } |
| 23 } |
| 24 if (seed == 0) { |
| 25 // We did not get a seed so far. As a fallback we do use the current time. |
| 26 seed = OS::GetCurrentTimeMicros(); |
| 27 } |
| 28 // Crank the next state a couple of times. |
| 29 _state = seed; |
| 30 NextState(); |
| 31 NextState(); |
| 32 NextState(); |
| 33 NextState(); |
| 34 } |
| 35 |
| 36 Random::~Random() { |
| 37 // Nothing to be done here. |
| 38 } |
| 39 |
| 40 // The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32. |
| 41 // http://en.wikipedia.org/wiki/Multiply-with-carry |
| 42 // The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1. |
| 43 void Random::NextState() { |
| 44 const uint64_t MASK_32 = 0xffffffff; |
| 45 const uint64_t A = 0xffffda61; |
| 46 |
| 47 uint64_t state_lo = _state & MASK_32; |
| 48 uint64_t state_hi = (_state >> 32) & MASK_32; |
| 49 _state = (A * state_lo) + state_hi; |
| 50 } |
| 51 |
| 52 |
| 53 uint32_t Random::NextUInt32() { |
| 54 const uint64_t MASK_32 = 0xffffffff; |
| 55 NextState(); |
| 56 return static_cast<uint32_t>(_state & MASK_32); |
| 57 } |
| 58 |
| 59 } // namespace dart |
OLD | NEW |