xoroshiro128p.h

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/*
 * Copyright 2018 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
// 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 <cstdint>
 
/*! \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