xorshift.h

// Copyright 2009-2023 NTESS. Under the terms
// of Contract DE-NA0003525 with NTESS, the U.S.
// Government retains certain rights in this software.
//
// Copyright (c) 2009-2023, NTESS
// All rights reserved.
//
// This file is part of the SST software package. For license
// information, see the LICENSE file in the top level directory of the
// distribution.

#ifndef SST_CORE_RNG_XORSHIFT_H
#define SST_CORE_RNG_XORSHIFT_H

#include "rng.h"

#include <stdint.h>
#include <sys/time.h>

#define XORSHIFT_UINT32_MAX 4294967295U
#define XORSHIFT_UINT64_MAX 18446744073709551615ULL
#define XORSHIFT_INT32_MAX  2147483647L
#define XORSHIFT_INT64_MAX  9223372036854775807LL

namespace SST {
namespace RNG {
/**
    \class XORShiftRNG xorshift.h "sst/core/rng/xorshift.h"

    Implements a lightweight RNG based on XOR-shift operations. We utilize the
    XORSHIFT algorithm from: http://en.wikipedia.org/wiki/Xorshift. This is a very
    lightweight and inexpensive RNG.

*/
class XORShiftRNG : public SST::RNG::Random
{

public:
    /**
        Create a new Xorshift RNG with a specified seed
        @param[in] seed The seed for this RNG
    */
    XORShiftRNG(unsigned int seed);

    /**
        Creates a new Xorshift using a random seed which is obtained from the system
        clock. Note this will give different results on different platforms and between
        runs.
    */
    XORShiftRNG();

    /**
        Generates the next random number as a double value between 0 and 1.
    */
    double nextUniform() override;

    /**
        Generates the next random number as an unsigned 32-bit integer
    */
    uint32_t generateNextUInt32() override;

    /**
        Generates the next random number as an unsigned 64-bit integer
    */
    uint64_t generateNextUInt64() override;

    /**
        Generates the next random number as a signed 64-bit integer
    */
    int64_t generateNextInt64() override;

    /**
        Generates the next random number as a signed 32-bit integer
    */
    int32_t generateNextInt32() override;

    /**
        Seed the XOR RNG
    */
    void seed(uint64_t newSeed);

    /**
        Destructor for Xorshift
    */
    ~XORShiftRNG();

protected:
    uint32_t x;
    uint32_t y;
    uint32_t z;
    uint32_t w;
};

} // namespace RNG
} // namespace SST

#endif // SST_CORE_RNG_XORSHIFT_H