xoroshiro128p.h

Go to the documentation of this file.

/*
 * Copyright 2018 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

// Built on XOROSHIRO128+ by David Blackman and Sebastiano Vigna who put this
// under CC-0, colloquially known as "public domain (or as close you get to that
// in your local legislation)" see
// http://xoroshiro.di.unimi.it/xoroshiro128plus.c
// Conversion to a local state (original used global state) done by Marcus
// Müller, 2018.
#ifndef INCLUDED_XOROSHIRO128P_H
#define INCLUDED_XOROSHIRO128P_H
#ifdef __cplusplus
extern "C" {
#endif

#include <stdint.h>

/*! \brief rotating left shift helper
 * According to the original authors, this will on most platforms reduce to a single instruction
 */
static inline uint64_t rotl(const uint64_t x, const int k) {
  return (x << k) | (x >> (64 - k));
}


/*! \brief generate the next random number and update the state.
 * This is the workhorse, here!
 */
static inline uint64_t xoroshiro128p_next(uint64_t *state) {
  const uint64_t s0 = state[0];
  uint64_t s1 = state[1];
  const uint64_t result = s0 + s1;

  s1 ^= s0;
  state[0] = rotl(s0, 55) ^ s1 ^ (s1 << 14); // a, b
  state[1] = rotl(s1, 36); // c

  return result;
}


/*! \brief Advance the internal state by 2^64 steps; useful when coordinating multiple independent RNGs
  This is the jump function for the generator. It is equivalent
  to 2^64 calls to next(); it can be used to generate 2^64
  non-overlapping subsequences for parallel computations. */
static inline void xoroshiro128p_jump(uint64_t *state) {
  static const uint64_t JUMP[] = { 0xbeac0467eba5facb, 0xd86b048b86aa9922 };

  uint64_t s0 = 0;
  uint64_t s1 = 0;
  for(unsigned int i = 0; i < sizeof (JUMP) / sizeof (*JUMP); ++i) {
    for(unsigned int b = 0; b < 64; ++b) {
      if (JUMP[i] & UINT64_C(1) << b) {
        s0 ^= state[0];
        s1 ^= state[1];
      }
      xoroshiro128p_next(state);
    }
  }

  state[0] = s0;
  state[1] = s1;
}

/*! \brief step of the SPLITMIX64 RNG; only used internally for seeding
 * This RNG isn't as good as XOROSHIRO128+, so it's only used to initialize a 128 bit state from a seed.
 */
static inline uint64_t splitmix64_next(uint64_t *state) {
  uint64_t z = (*state += 0x9e3779b97f4a7c15);
  z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
  z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
  return z ^ (z >> 31);
}

/*! \brief Seed the 128 bit state from a 64 bit seed
 */
static inline void xoroshiro128p_seed(uint64_t *state, const uint64_t seed) {
  state[0] = seed;
  state[1] = splitmix64_next(state);
  xoroshiro128p_jump(state);
}
#ifdef __cplusplus
}
#endif
#endif // Include guard