rocrand_threefry4_impl.h

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/*
Copyright 2010-2011, D. E. Shaw Research.
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  contributors may be used to endorse or promote products derived from
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#ifndef ROCRAND_THREEFRY4_IMPL_H_
#define ROCRAND_THREEFRY4_IMPL_H_

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

#include "rocrand/rocrand_threefry_common.h"
#include <rocrand/rocrand_common.h>

#ifndef THREEFRY4x32_DEFAULT_ROUNDS
    #define THREEFRY4x32_DEFAULT_ROUNDS 20
#endif

#ifndef THREEFRY4x64_DEFAULT_ROUNDS
    #define THREEFRY4x64_DEFAULT_ROUNDS 20
#endif

/* These are the R_256 constants from the Threefish reference sources
   with names changed to R_64x4... */
static constexpr __device__ int THREEFRY_ROTATION_64_4[8][2] = {
    {14, 16},
    {52, 57},
    {23, 40},
    { 5, 37},
    {25, 33},
    {46, 12},
    {58, 22},
    {32, 32}
};

/* Output from skein_rot_search: (srs-B128-X5000.out)
// Random seed = 1. BlockSize = 64 bits. sampleCnt =  1024. rounds =  8, minHW_or=28
// Start: Mon Aug 24 22:41:36 2009
// ...
// rMin = 0.472. #0A4B[*33] [CRC=DD1ECE0F. hw_OR=31. cnt=16384. blkSize= 128].format    */
static constexpr __device__ int THREEFRY_ROTATION_32_4[8][2] = {
    {10, 26},
    {11, 21},
    {13, 27},
    {23,  5},
    { 6, 20},
    {17, 11},
    {25, 10},
    {18, 20}
};

namespace rocrand_device
{

template<class value>
FQUALIFIERS int threefry_rotation_array(int indexX, int indexY);

template<>
FQUALIFIERS int threefry_rotation_array<unsigned int>(int indexX, int indexY)
{
    return THREEFRY_ROTATION_32_4[indexX][indexY];
};

template<>
FQUALIFIERS int threefry_rotation_array<unsigned long long>(int indexX, int indexY)
{
    return THREEFRY_ROTATION_64_4[indexX][indexY];
};

template<typename state_value, typename value, unsigned int Nrounds>
class threefry_engine4_base
{
public:
    struct threefry_state_4
    {
        state_value  counter;
        state_value  key;
        state_value  result;
        unsigned int substate;
    };

    FQUALIFIERS void discard(unsigned long long offset)
    {
        this->discard_impl(offset);
        this->m_state.result = this->threefry_rounds(m_state.counter, m_state.key);
    }

    FQUALIFIERS void discard_subsequence(unsigned long long subsequence)
    {
        this->discard_subsequence_impl(subsequence);
        m_state.result = this->threefry_rounds(m_state.counter, m_state.key);
    }

    FQUALIFIERS value operator()()
    {
        return this->next();
    }

    FQUALIFIERS value next()
    {
#if defined(__HIP_PLATFORM_AMD__)
        value ret = m_state.result.data[m_state.substate];
#else
        value ret = (&m_state.result.x)[m_state.substate];
#endif
        m_state.substate++;
        if(m_state.substate == 4)
        {
            m_state.substate = 0;
            m_state.counter  = this->bump_counter(m_state.counter);
            m_state.result   = this->threefry_rounds(m_state.counter, m_state.key);
        }
        return ret;
    }

    FQUALIFIERS state_value next4()
    {
        state_value ret = m_state.result;
        m_state.counter = this->bump_counter(m_state.counter);
        m_state.result  = this->threefry_rounds(m_state.counter, m_state.key);

        return this->interleave(ret, m_state.result);
    }

protected:
    FQUALIFIERS state_value threefry_rounds(state_value counter, state_value key)
    {
        state_value X;
        value       ks[4 + 1];

        static_assert(Nrounds <= 72, "72 or less only supported in threefry rounds");

        ks[4] = skein_ks_parity<value>();

        ks[0] = key.x;
        ks[1] = key.y;
        ks[2] = key.z;
        ks[3] = key.w;

        X.x = counter.x;
        X.y = counter.y;
        X.z = counter.z;
        X.w = counter.w;

        ks[4] ^= key.x;
        ks[4] ^= key.y;
        ks[4] ^= key.z;
        ks[4] ^= key.w;

        /* Insert initial key before round 0 */
        X.x += ks[0];
        X.y += ks[1];
        X.z += ks[2];
        X.w += ks[3];

        for(unsigned int round_idx = 0; round_idx < Nrounds; round_idx++)
        {
            int rot_0 = threefry_rotation_array<value>(round_idx & 7u, 0);
            int rot_1 = threefry_rotation_array<value>(round_idx & 7u, 1);
            if((round_idx & 2u) == 0)
            {
                X.x += X.y;
                X.y = rotl<value>(X.y, rot_0);
                X.y ^= X.x;
                X.z += X.w;
                X.w = rotl<value>(X.w, rot_1);
                X.w ^= X.z;
            }
            else
            {
                X.x += X.w;
                X.w = rotl<value>(X.w, rot_0);
                X.w ^= X.x;
                X.z += X.y;
                X.y = rotl<value>(X.y, rot_1);
                X.y ^= X.z;
            }

            if((round_idx & 3u) == 3)
            {
                unsigned int inject_idx = round_idx / 4;
                // InjectKey(r = 1 + inject_idx)
                X.x += ks[(1 + inject_idx) % 5];
                X.y += ks[(2 + inject_idx) % 5];
                X.z += ks[(3 + inject_idx) % 5];
                X.w += ks[(4 + inject_idx) % 5];
                X.w += 1 + inject_idx;
            }
        }

        return X;
    }

    FQUALIFIERS void discard_impl(unsigned long long offset)
    {
        // Adjust offset for subset
        m_state.substate += offset & 3;
        unsigned long long counter_offset = offset / 4;
        counter_offset += m_state.substate < 4 ? 0 : 1;
        m_state.substate += m_state.substate < 4 ? 0 : -4;
        // Discard states
        this->discard_state(counter_offset);
    }

    FQUALIFIERS void discard_subsequence_impl(unsigned long long subsequence)
    {
        value lo, hi;
        ::rocrand_device::detail::split_ull(lo, hi, subsequence);

        value old_counter = m_state.counter.z;
        m_state.counter.z += lo;
        m_state.counter.w += hi + (m_state.counter.z < old_counter ? 1 : 0);
    }

    FQUALIFIERS void discard_state(unsigned long long offset)
    {
        value lo, hi;
        ::rocrand_device::detail::split_ull(lo, hi, offset);

        state_value old_counter = m_state.counter;
        m_state.counter.x += lo;
        m_state.counter.y += hi + (m_state.counter.x < old_counter.x ? 1 : 0);
        m_state.counter.z += (m_state.counter.y < old_counter.y ? 1 : 0);
        m_state.counter.w += (m_state.counter.z < old_counter.z ? 1 : 0);
    }

    FQUALIFIERS static state_value bump_counter(state_value counter)
    {
        counter.x++;
        value add = counter.x == 0 ? 1 : 0;
        counter.y += add;
        add = counter.y == 0 ? add : 0;
        counter.z += add;
        add = counter.z == 0 ? add : 0;
        counter.w += add;
        return counter;
    }

    FQUALIFIERS state_value interleave(const state_value prev, const state_value next) const
    {
        switch(m_state.substate)
        {
            case 0: return prev;
            case 1: return state_value{prev.y, prev.z, prev.w, next.x};
            case 2: return state_value{prev.z, prev.w, next.x, next.y};
            case 3: return state_value{prev.w, next.x, next.y, next.z};
        }
        __builtin_unreachable();
    }

protected:
    threefry_state_4 m_state;
}; // threefry_engine4_base class

} // end namespace rocrand_device

#endif // ROCRAND_THREEFRY4_IMPL_H_