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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file contains the definition of the RandomState class, a fast and
/// lightweight pseudo-random number generator.
///
/// The implementation is based on the xorshift* generator, seeded using the
/// SplitMix64 generator for robust initialization. For more details on the
/// algorithm, see: https://en.wikipedia.org/wiki/Xorshift
///
//===----------------------------------------------------------------------===//
#ifndef MATHTEST_RANDOMSTATE_HPP
#define MATHTEST_RANDOMSTATE_HPP
#include <cstdint>
struct SeedTy {
uint64_t Value;
};
class [[nodiscard]] RandomState {
uint64_t State;
[[nodiscard]] static constexpr uint64_t splitMix64(uint64_t X) noexcept {
X += 0x9E3779B97F4A7C15ULL;
X = (X ^ (X >> 30)) * 0xBF58476D1CE4E5B9ULL;
X = (X ^ (X >> 27)) * 0x94D049BB133111EBULL;
X = (X ^ (X >> 31));
return X ? X : 0x9E3779B97F4A7C15ULL;
}
public:
explicit constexpr RandomState(SeedTy Seed) noexcept
: State(splitMix64(Seed.Value)) {}
inline uint64_t next() noexcept {
uint64_t X = State;
X ^= X >> 12;
X ^= X << 25;
X ^= X >> 27;
State = X;
return X * 0x2545F4914F6CDD1DULL;
}
};
#endif // MATHTEST_RANDOMSTATE_HPP
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