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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8///9/// \file10/// This file contains the definition of the RandomState class, a fast and11/// lightweight pseudo-random number generator.12///13/// The implementation is based on the xorshift* generator, seeded using the14/// SplitMix64 generator for robust initialization. For more details on the15/// algorithm, see: https://en.wikipedia.org/wiki/Xorshift16///17//===----------------------------------------------------------------------===//18 19#ifndef MATHTEST_RANDOMSTATE_HPP20#define MATHTEST_RANDOMSTATE_HPP21 22#include <cstdint>23 24struct SeedTy {25 uint64_t Value;26};27 28class [[nodiscard]] RandomState {29 uint64_t State;30 31 [[nodiscard]] static constexpr uint64_t splitMix64(uint64_t X) noexcept {32 X += 0x9E3779B97F4A7C15ULL;33 X = (X ^ (X >> 30)) * 0xBF58476D1CE4E5B9ULL;34 X = (X ^ (X >> 27)) * 0x94D049BB133111EBULL;35 X = (X ^ (X >> 31));36 return X ? X : 0x9E3779B97F4A7C15ULL;37 }38 39public:40 explicit constexpr RandomState(SeedTy Seed) noexcept41 : State(splitMix64(Seed.Value)) {}42 43 inline uint64_t next() noexcept {44 uint64_t X = State;45 X ^= X >> 12;46 X ^= X << 25;47 X ^= X >> 27;48 State = X;49 return X * 0x2545F4914F6CDD1DULL;50 }51};52 53#endif // MATHTEST_RANDOMSTATE_HPP54