iposva@google.com
070d3dedf7
VM internals. This PRNG is not used to generate random numbers in Dart code. - Use the PRNG to generate JIT cookies for large constants if needed during assembly. - Add the possibility to set an external entropy source for the PRNG through the C API. R=asiva@google.com Review URL: https://codereview.chromium.org//59773007 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@29950 260f80e4-7a28-3924-810f-c04153c831b5
60 lines
1.6 KiB
C++
60 lines
1.6 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/flags.h"
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#include "vm/isolate.h"
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namespace dart {
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DEFINE_FLAG(int, random_seed, 0, "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 = Isolate::entropy_source_callback();
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if (callback != NULL) {
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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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// 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() {
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// Nothing to be done here.
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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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void 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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}
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uint32_t Random::NextUInt32() {
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const uint64_t MASK_32 = 0xffffffff;
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NextState();
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return static_cast<uint32_t>(_state & MASK_32);
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}
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} // namespace dart
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