Line data    Source code

       1             : // Copyright (c) 2022 The Bitcoin Core developers
       2             : // Distributed under the MIT software license, see the accompanying
       3             : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4             : 
       5             : #ifndef BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H
       6             : #define BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H
       7             : 
       8             : #include <cstdint>
       9             : #include <limits>
      10             : 
      11             : /** xoroshiro128++ PRNG. Extremely fast, not appropriate for cryptographic purposes.
      12             :  *
      13             :  * Memory footprint is 128bit, period is 2^128 - 1.
      14             :  * This class is not thread-safe.
      15             :  *
      16             :  * Reference implementation available at https://prng.di.unimi.it/xoroshiro128plusplus.c
      17             :  * See https://prng.di.unimi.it/
      18             :  */
      19             : class XoRoShiRo128PlusPlus
      20             : {
      21             :     uint64_t m_s0;
      22             :     uint64_t m_s1;
      23             : 
      24           0 :     [[nodiscard]] constexpr static uint64_t rotl(uint64_t x, int n)
      25             :     {
      26           0 :         return (x << n) | (x >> (64 - n));
      27             :     }
      28             : 
      29           0 :     [[nodiscard]] constexpr static uint64_t SplitMix64(uint64_t& seedval) noexcept
      30             :     {
      31           0 :         uint64_t z = (seedval += UINT64_C(0x9e3779b97f4a7c15));
      32           0 :         z = (z ^ (z >> 30U)) * UINT64_C(0xbf58476d1ce4e5b9);
      33           0 :         z = (z ^ (z >> 27U)) * UINT64_C(0x94d049bb133111eb);
      34           0 :         return z ^ (z >> 31U);
      35             :     }
      36             : 
      37             : public:
      38             :     using result_type = uint64_t;
      39             : 
      40           0 :     constexpr explicit XoRoShiRo128PlusPlus(uint64_t seedval) noexcept
      41           0 :         : m_s0(SplitMix64(seedval)), m_s1(SplitMix64(seedval))
      42             :     {
      43           0 :     }
      44             : 
      45             :     // no copy - that is dangerous, we don't want accidentally copy the RNG and then have two streams
      46             :     // with exactly the same results. If you need a copy, call copy().
      47             :     XoRoShiRo128PlusPlus(const XoRoShiRo128PlusPlus&) = delete;
      48             :     XoRoShiRo128PlusPlus& operator=(const XoRoShiRo128PlusPlus&) = delete;
      49             : 
      50             :     // allow moves
      51             :     XoRoShiRo128PlusPlus(XoRoShiRo128PlusPlus&&) = default;
      52             :     XoRoShiRo128PlusPlus& operator=(XoRoShiRo128PlusPlus&&) = default;
      53             : 
      54             :     ~XoRoShiRo128PlusPlus() = default;
      55             : 
      56           0 :     constexpr result_type operator()() noexcept
      57             :     {
      58           0 :         uint64_t s0 = m_s0, s1 = m_s1;
      59           0 :         const uint64_t result = rotl(s0 + s1, 17) + s0;
      60           0 :         s1 ^= s0;
      61           0 :         m_s0 = rotl(s0, 49) ^ s1 ^ (s1 << 21);
      62           0 :         m_s1 = rotl(s1, 28);
      63           0 :         return result;
      64             :     }
      65             : 
      66             :     static constexpr result_type min() noexcept { return std::numeric_limits<result_type>::min(); }
      67             :     static constexpr result_type max() noexcept { return std::numeric_limits<result_type>::max(); }
      68             :     static constexpr double entropy() noexcept { return 0.0; }
      69             : };
      70             : 
      71             : #endif // BITCOIN_TEST_UTIL_XOROSHIRO128PLUSPLUS_H