Program Listing for File rocrand_sobol64.h

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// Copyright (c) 2021-2022 Advanced Micro Devices, Inc. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// THE SOFTWARE.

#ifndef ROCRAND_SOBOL64_H_
#define ROCRAND_SOBOL64_H_

#ifndef FQUALIFIERS
#define FQUALIFIERS __forceinline__ __device__
#endif // FQUALIFIERS_

#include "rocrand/rocrand_common.h"

namespace rocrand_device {

template<bool UseSharedVectors>
struct sobol64_state
{
    unsigned long long int d;
    unsigned long long int i;
    unsigned long long int vectors[64];

    FQUALIFIERS
    sobol64_state() { }

    FQUALIFIERS
    sobol64_state(const unsigned long long int d,
                  const unsigned long long int i,
                  const unsigned long long int * vectors)
        : d(d), i(i)
    {
        for(int k = 0; k < 64; k++)
        {
            this->vectors[k] = vectors[k];
        }
    }
};

template<>
struct sobol64_state<true>
{
    unsigned long long int d;
    unsigned long long int i;
    const unsigned long long int * vectors;

    FQUALIFIERS
    sobol64_state() { }

    FQUALIFIERS
    sobol64_state(const unsigned long long int d,
                  const unsigned long long int i,
                  const unsigned long long int * vectors)
        : d(d), i(i), vectors(vectors) { }
};

template<bool UseSharedVectors>
class sobol64_engine
{
public:

    typedef struct sobol64_state<UseSharedVectors> sobol64_state;

    FQUALIFIERS
    sobol64_engine() { }

    FQUALIFIERS
    sobol64_engine(const unsigned long long int* vectors, const unsigned long long int offset)
        : m_state(0, 0, vectors)
    {
        discard_state(offset);
    }

    FQUALIFIERS
    void discard(unsigned long long int offset)
    {
        discard_state(offset);
    }

    FQUALIFIERS
    void discard()
    {
        discard_state();
    }

    FQUALIFIERS
    void discard_stride(unsigned long long int stride)
    {
        discard_state_power2(stride);
    }

    FQUALIFIERS
    unsigned long long int operator()()
    {
        return this->next();
    }

    FQUALIFIERS
    unsigned long long int next()
    {
        unsigned long long int p = m_state.d;
        discard_state();
        return p;
    }

    FQUALIFIERS
    unsigned long long int current()
    {
        return m_state.d;
    }

protected:
    // Advances the internal state by offset times.
    FQUALIFIERS
    void discard_state(unsigned long long int offset)
    {
        m_state.i += offset;
        const unsigned long long int g = m_state.i ^ (m_state.i >> 1ull);
        m_state.d = 0;
        for(int i = 0; i < 64; i++)
        {
            m_state.d ^= (g & (1ull << i) ? m_state.vectors[i] : 0ull);
        }
    }

    // Advances the internal state to the next state
    FQUALIFIERS
    void discard_state()
    {
        m_state.d ^= m_state.vectors[rightmost_zero_bit(m_state.i)];
        m_state.i++;
    }

    FQUALIFIERS
    void discard_state_power2(unsigned long long int stride)
    {
        // Leap frog
        //
        // T Bradley, J Toit, M Giles, R Tong, P Woodhams
        // Parallelisation Techniques for Random Number Generators
        // GPU Computing Gems, 2011
        //
        // For power of 2 jumps only 2 bits in Gray code change values
        // All bits lower than log2(stride) flip 2, 4... times, i.e.
        // do not change their values.

        // log2(stride) bit
        m_state.d ^= m_state.vectors[rightmost_zero_bit(~stride) - 1];
        // the rightmost zero bit of i, not including the lower log2(stride) bits
        m_state.d ^= m_state.vectors[rightmost_zero_bit(m_state.i | (stride - 1))];
        m_state.i += stride;
    }

    // Returns the index of the rightmost zero bit in the binary expansion of
    // x (Gray code of the current element's index)
    // NOTE changing unsigned long long int to unit64_t will cause compile failure on device
    FQUALIFIERS
    unsigned int rightmost_zero_bit(unsigned long long int x)
    {
        #if defined(__HIP_DEVICE_COMPILE__)
        unsigned int z = __ffsll(~x);
        return z ? z - 1 : 0;
        #else
        if(x == 0)
            return 0;
        unsigned long long int y = x;
        unsigned long long int z = 1;
        while(y & 1)
        {
            y >>= 1;
            z++;
        }
        return z - 1;
        #endif
    }

protected:
    // State
    sobol64_state m_state;

}; // sobol64_engine class

} // end namespace rocrand_device

typedef rocrand_device::sobol64_engine<false> rocrand_state_sobol64;

FQUALIFIERS
void rocrand_init(const unsigned long long int * vectors,
                  const unsigned int offset,
                  rocrand_state_sobol64 * state)
{
    *state = rocrand_state_sobol64(vectors, offset);
}

FQUALIFIERS
unsigned long long int rocrand(rocrand_state_sobol64 * state)
{
    return state->next();
}

FQUALIFIERS
void skipahead(unsigned long long int offset, rocrand_state_sobol64* state)
{
    return state->discard(offset);
}

 // end of group rocranddevice
#endif // ROCRAND_sobol64_H_