Line data    Source code

       1             : // Copyright (c) 2021-2023 The Dash 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_LCG_H
       6             : #define BITCOIN_TEST_LCG_H
       7             : 
       8             : #include <cstdint>
       9             : 
      10             : // Simple 32-bit linear congruential generator with 64-bit internal state,
      11             : // often called as "MMIX by Donald Knuth". Knuth attributes the multiplier
      12             : // to C. E. Haynes and the increment is not crucial (it only need be odd).
      13             : // Knuth, Donald (1997). Seminumerical Algorithms Vol2. Sec 3.3.4. 3rd Ed.
      14             : //
      15             : // Low bits have short period, hence we use high bits which should have
      16             : // the same period as the entire generator (2^64).
      17             : class MMIXLinearCongruentialGenerator {
      18             :     uint64_t state;
      19             : 
      20             : public:
      21           2 :     MMIXLinearCongruentialGenerator(uint64_t initialstate = 0)
      22           2 :         : state(initialstate) {}
      23             : 
      24             :     // pseudorandom, except the first value returned is the seed provided
      25             :     // (thus starting with 0, by default)
      26        4096 :     uint32_t next() {
      27        4096 :         uint32_t ret = state >> 32;
      28        4096 :         state = state * 6364136223846793005 + 1442695040888963407;
      29        4096 :         return ret;
      30             :     }
      31             : };
      32             : 
      33             : #endif // BITCOIN_TEST_LCG_H