Ryan Macnak
f1aa58931d
The per Thread instance is sufficient. TEST=ci Change-Id: Iff2c4279937637089f7ae4194cb1097b5e6eef67 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/452881 Commit-Queue: Ryan Macnak <rmacnak@google.com> Reviewed-by: Alexander Aprelev <aam@google.com>
76 lines
1.9 KiB
C++
76 lines
1.9 KiB
C++
// Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#include "vm/random.h"
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#include "vm/dart.h"
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#include "vm/flags.h"
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#include "vm/os.h"
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namespace dart {
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DEFINE_FLAG(uint64_t,
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random_seed,
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0,
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"Override the random seed for debugging.");
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Random::Random() {
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uint64_t seed = FLAG_random_seed;
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if (seed == 0) {
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Dart_EntropySource callback = Dart::entropy_source_callback();
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if (callback != nullptr) {
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if (!callback(reinterpret_cast<uint8_t*>(&seed), sizeof(seed))) {
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// Callback failed. Reset the seed to 0.
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seed = 0;
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}
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}
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}
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if (seed == 0) {
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// We did not get a seed so far. As a fallback we do use the current time.
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seed = OS::GetCurrentTimeMicros();
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}
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Initialize(seed);
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}
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void Random::Initialize(uint64_t seed) {
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ASSERT(seed != 0);
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// Crank the next state a couple of times.
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state_ = seed;
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NextState();
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NextState();
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NextState();
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NextState();
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}
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Random::Random(uint64_t seed) {
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Initialize(seed);
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}
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// The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32.
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// http://en.wikipedia.org/wiki/Multiply-with-carry
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// The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1.
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uint64_t Random::NextState() {
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const uint64_t MASK_32 = 0xffffffff;
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const uint64_t A = 0xffffda61;
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uint64_t state_lo = state_ & MASK_32;
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uint64_t state_hi = (state_ >> 32) & MASK_32;
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state_ = (A * state_lo) + state_hi;
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return state_;
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}
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uint32_t Random::NextUInt32() {
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const uint64_t MASK_32 = 0xffffffff;
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return static_cast<uint32_t>(NextState() & MASK_32);
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}
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double Random::NextDouble() {
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uint64_t mantissa = NextUInt64() & 0xFFFFFFFFFFFFF;
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// The exponent value 0 in biased form.
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const uint64_t exp = 1023;
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return bit_cast<double>(exp << 52 | mantissa) - 1.0;
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}
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} // namespace dart
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