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File indexing completed on 2026-10-26 09:34:38
0001 //------------------------------- -*- C++ -*- -------------------------------// 0002 // Copyright Celeritas contributors: see top-level COPYRIGHT file for details 0003 // SPDX-License-Identifier: (Apache-2.0 OR MIT) 0004 //---------------------------------------------------------------------------// 0005 //! \file corecel/random/engine/SplitMix64.hh 0006 //---------------------------------------------------------------------------// 0007 #pragma once 0008 0009 #include <cstdint> 0010 0011 #include "corecel/Macros.hh" 0012 0013 namespace celeritas 0014 { 0015 0016 //---------------------------------------------------------------------------// 0017 /*! 0018 * \brief RNG for initializing the state for other RNGs 0019 * 0020 * See https://prng.di.unimi.it for a details of the SplitMix64 engine 0021 */ 0022 class SplitMix64 0023 { 0024 public: 0025 // Construct the SplitMix64 class with the given seed 0026 inline CELER_FUNCTION explicit SplitMix64(std::uint64_t seed); 0027 0028 // Produce a random number 0029 inline CELER_FUNCTION std::uint64_t operator()(); 0030 0031 // Advance the state forward one sample 0032 inline CELER_FUNCTION void advance(); 0033 0034 // XOR this state with another 0035 inline CELER_FUNCTION void xor_state(std::uint64_t state); 0036 0037 private: 0038 // SplitMix64 State 0039 std::uint64_t state_; 0040 }; 0041 0042 //---------------------------------------------------------------------------// 0043 // INLINE DEFINITIONS 0044 //---------------------------------------------------------------------------// 0045 /*! 0046 * Construct the SplitMix64 engine with the given seed. 0047 */ 0048 CELER_FUNCTION SplitMix64::SplitMix64(std::uint64_t seed) : state_(seed) 0049 { 0050 /* * */ 0051 } 0052 0053 //---------------------------------------------------------------------------// 0054 /*! 0055 * Generate a 64-bit pseudorandom number using the SplitMix64 engine. 0056 * 0057 * See https://prng.di.unimi.it for a description of the method. 0058 */ 0059 CELER_FUNCTION std::uint64_t SplitMix64::operator()() 0060 { 0061 this->advance(); 0062 std::uint64_t z = state_; 0063 z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ull; 0064 z = (z ^ (z >> 27)) * 0x94d049bb133111ebull; 0065 return z ^ (z >> 31); 0066 } 0067 0068 //---------------------------------------------------------------------------// 0069 /*! 0070 * \brief Advance the state forward by one sample 0071 */ 0072 CELER_FUNCTION void SplitMix64::advance() 0073 { 0074 state_ += 0x9e3779b97f4a7c15ull; 0075 } 0076 0077 //---------------------------------------------------------------------------// 0078 /*! 0079 * Perform a XOR operation of this state with another state. 0080 */ 0081 CELER_FUNCTION void SplitMix64::xor_state(std::uint64_t state) 0082 { 0083 state_ ^= state; 0084 } 0085 0086 //---------------------------------------------------------------------------// 0087 } // namespace celeritas
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