blob: 1451cf2a61a81f3d3d9ed5c603d83d0a4fca8098 [file] [log] [blame]
// 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