| /* |
| * 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()) |
| { |
| 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 unsigned lowOffset() { return OBJECT_OFFSETOF(WeakRandom, m_low); } |
| static 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; |