xoshiro_256_star_star.cpp

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/*
 *  SPDX-FileCopyrightText: Copyright 2021, Siavash Ameli <sameli@berkeley.edu>
 *  SPDX-License-Identifier: BSD-3-Clause
 *  SPDX-FileType: SOURCE
 *
 *  This program is free software: you can redistribute it and/or modify it
 *  under the terms of the license found in the LICENSE.txt file in the root
 *  directory of this source tree.
 */
 
 
// =======
// Headers
// =======
 
#include "./xoshiro_256_star_star.h"
#include <cstdlib>  // NULL
#include "./split_mix_64.h"  // SplitMix64
 
// stdint.h in old compilers (e.g. gcc 4.4.7) does not declare UINT64_C macro.
#ifndef UINT64_C
    #define UINT64_C(c) static_cast<uint64_t>(c)
#endif
 
 
// ===========
// Constructor
// ===========
 
Xoshiro256StarStar::Xoshiro256StarStar(const int64_t seed):
    state(NULL)
{
    // Allocate state
    this->state = new uint64_t[4];
 
    // Initializing SplitMix64 random generator
    SplitMix64 split_mix_64(seed);
 
    for (int i=0; i < 4; ++i)
    {
        this->state[i] = split_mix_64.next();
    }
}
 
 
// ==========
// Destructor
// ==========
 
 
Xoshiro256StarStar::~Xoshiro256StarStar()
{
    if (this->state != NULL)
    {
        delete[] this->state;
        this->state = NULL;
    }
}
 
 
// ====
// next
// ====
 
 
uint64_t Xoshiro256StarStar::next()
{
    const uint64_t result = this->rotation_left(this->state[1] * 5, 7) * 9;
 
    const uint64_t t = this->state[1] << 17;
 
    this->state[2] ^= this->state[0];
    this->state[3] ^= this->state[1];
    this->state[1] ^= this->state[2];
    this->state[0] ^= this->state[3];
 
    this->state[2] ^= t;
 
    this->state[3] = this->rotation_left(this->state[3], 45);
 
    return result;
}
 
 
// ====
// jump
// ====
 
 
void Xoshiro256StarStar::jump()
{
    static const uint64_t JUMP[] = {
        0x180ec6d33cfd0aba,
        0xd5a61266f0c9392c,
        0xa9582618e03fc9aa,
        0x39abdc4529b1661c};
 
    uint64_t s0 = 0;
    uint64_t s1 = 0;
    uint64_t s2 = 0;
    uint64_t s3 = 0;
 
    for (unsigned int i = 0; i < sizeof(JUMP) / sizeof(*JUMP); ++i)
    {
        for (int b = 0; b < 64; ++b)
        {
            if (JUMP[i] & UINT64_C(1) << b)
            {
                s0 ^= this->state[0];
                s1 ^= this->state[1];
                s2 ^= this->state[2];
                s3 ^= this->state[3];
            }
 
            this->next();
        }
    }
 
    this->state[0] = s0;
    this->state[1] = s1;
    this->state[2] = s2;
    this->state[3] = s3;
}
 
 
// =========
// long jump
// =========
 
 
void Xoshiro256StarStar::long_jump()
{
    static const uint64_t LONG_JUMP[] = {
        0x76e15d3efefdcbbf,
        0xc5004e441c522fb3,
        0x77710069854ee241,
        0x39109bb02acbe635};
 
    uint64_t s0 = 0;
    uint64_t s1 = 0;
    uint64_t s2 = 0;
    uint64_t s3 = 0;
 
    for (unsigned int i = 0; i < sizeof(LONG_JUMP) / sizeof(*LONG_JUMP); ++i)
    {
        for (int b = 0; b < 64; ++b)
        {
            if (LONG_JUMP[i] & UINT64_C(1) << b)
            {
                s0 ^= this->state[0];
                s1 ^= this->state[1];
                s2 ^= this->state[2];
                s3 ^= this->state[3];
            }
 
            this->next();
        }
    }
 
    this->state[0] = s0;
    this->state[1] = s1;
    this->state[2] = s2;
    this->state[3] = s3;
}
 
 
// ===========
// rotate left
// ===========
 
 
inline uint64_t Xoshiro256StarStar::rotation_left(
        const uint64_t x,
        int k)
{
    return (x << k) | (x >> (64 - k));
}