Line data    Source code

       1             : /*
       2             : This 64 bit pseudo random number generator is based on the engine
       3             : written by Sebastiano Vigna from Dipartimento di Informatica of the
       4             : Università degli Studi di Milano.  The original source code can be
       5             : found here http://xoshiro.di.unimi.it/xoshiro256starstar.c.  The
       6             : engine is supposed to perform very well on various random engine
       7             : benchmarks.
       8             : The original author offered his work to the public domain per the
       9             : following original comment.
      10             : */
      11             : 
      12             : /*  Written in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
      13             : 
      14             : To the extent possible under law, the author has dedicated all copyright
      15             : and related and neighboring rights to this software to the public domain
      16             : worldwide. This software is distributed without any warranty.
      17             : 
      18             : See <http://creativecommons.org/publicdomain/zero/1.0/>. */
      19             : 
      20             : typedef uint64_t random_state_engine[4];
      21             : 
      22             : static inline uint64_t
      23    41997278 : rotl(const uint64_t x, int k)
      24             : {
      25    41997278 :         return (x << k) | (x >> (64 - k));
      26             : }
      27             : 
      28             : static inline void
      29         663 : init_random_state_engine(random_state_engine engine, uint64_t seed)
      30             : {
      31        3315 :         for (int i = 0; i < 4; i++) {
      32             :                 /* we use the splitmix64 generator to generate the 4
      33             :                  * values in the state array from the given seed.
      34             :                  * This code is adapted from
      35             :                  * http://xoshiro.di.unimi.it/splitmix64.c which was
      36             :                  * put in the public domain in the same way as the
      37             :                  * "next" function below. */
      38        2652 :                 uint64_t z = (seed += 0x9e3779b97f4a7c15);
      39        2652 :                 z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
      40        2652 :                 z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
      41        2652 :                 engine[i] = z ^ (z >> 31);
      42             :         }
      43         663 : }
      44             : 
      45             : static inline uint64_t
      46    41997278 : next(random_state_engine rse)
      47             : {
      48    41997278 :         const uint64_t output = rotl(rse[1] * 5, 7) * 9;
      49             : 
      50    41997278 :         const uint64_t t = rse[1] << 17;
      51             : 
      52    41997278 :         rse[2] ^= rse[0];
      53    41997278 :         rse[3] ^= rse[1];
      54    41997278 :         rse[1] ^= rse[2];
      55    41997278 :         rse[0] ^= rse[3];
      56             : 
      57    41997278 :         rse[2] ^= t;
      58             : 
      59    41997278 :         rse[3] = rotl(rse[3], 45);
      60             : 
      61    41997278 :         return output;
      62             : }