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