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/*
* Copyright (C) 2009, 2015 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Vigna, Sebastiano (2014). "Further scramblings of Marsaglia's xorshift
* generators". arXiv:1404.0390 (http://arxiv.org/abs/1404.0390)
*
* See also https://en.wikipedia.org/wiki/Xorshift.
*/
#pragma once
#include <limits.h>
#include <wtf/CryptographicallyRandomNumber.h>
#include <wtf/StdLibExtras.h>
namespace WTF {
// The code used to generate random numbers are inlined manually in JIT code.
// So it needs to stay in sync with the JIT one.
class WeakRandom final {
WTF_MAKE_FAST_ALLOCATED;
public:
WeakRandom(unsigned seed = cryptographicallyRandomNumber<unsigned>())
{
setSeed(seed);
}
void setSeed(unsigned seed)
{
m_seed = seed;
// A zero seed would cause an infinite series of zeroes.
if (!seed)
seed = 1;
m_low = seed;
m_high = seed;
advance();
}
unsigned seed() const { return m_seed; }
double get()
{
uint64_t value = advance() & ((1ULL << 53) - 1);
return value * (1.0 / (1ULL << 53));
}
unsigned getUint32()
{
return static_cast<unsigned>(advance());
}
unsigned getUint32(unsigned limit)
{
if (limit <= 1)
return 0;
uint64_t cutoff = (static_cast<uint64_t>(std::numeric_limits<unsigned>::max()) + 1) / limit * limit;
for (;;) {
uint64_t value = getUint32();
if (value >= cutoff)
continue;
return value % limit;
}
}
uint64_t getUint64()
{
return advance();
}
bool returnTrueWithProbability(double probability)
{
ASSERT(0.0 <= probability && probability <= 1.0);
if (!probability)
return false;
double value = getUint32();
if (value <= static_cast<double>(std::numeric_limits<unsigned>::max()) * probability)
return true;
return false;
}
static constexpr unsigned lowOffset() { return OBJECT_OFFSETOF(WeakRandom, m_low); }
static constexpr unsigned highOffset() { return OBJECT_OFFSETOF(WeakRandom, m_high); }
static constexpr uint64_t nextState(uint64_t x, uint64_t y)
{
x ^= x << 23;
x ^= x >> 17;
x ^= y ^ (y >> 26);
return x;
}
static constexpr uint64_t generate(unsigned seed)
{
if (!seed)
seed = 1;
uint64_t low = seed;
uint64_t high = seed;
high = nextState(low, high);
return low + high;
}
private:
uint64_t advance()
{
uint64_t x = m_low;
uint64_t y = m_high;
m_low = y;
m_high = nextState(x, y);
return m_high + m_low;
}
unsigned m_seed;
uint64_t m_low;
uint64_t m_high;
};
} // namespace WTF
using WTF::WeakRandom;
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