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 // Copyright (c) 2021-2024 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
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
  
 #ifndef ROCRAND_SOBOL64_H_
 #define ROCRAND_SOBOL64_H_
  
 #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];
  
     __forceinline__ __device__ __host__ sobol64_state() : d(), i(), vectors() {}
  
     __forceinline__ __device__ __host__ 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;
  
     __forceinline__ __device__ __host__ sobol64_state() : d(), i(), vectors() {}
  
     __forceinline__ __device__ __host__ 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;
  
     __forceinline__ __device__ __host__ sobol64_engine() {}
  
     __forceinline__ __device__ __host__ sobol64_engine(const unsigned long long int* vectors,
                                                        const unsigned long long int  offset)
         : m_state(0, 0, vectors)
     {
         discard_state(offset);
     }
  
     __forceinline__ __device__ __host__ void discard(unsigned long long int offset)
     {
         discard_state(offset);
     }
  
     __forceinline__ __device__ __host__ void discard()
     {
         discard_state();
     }
  
     __forceinline__ __device__ __host__ void discard_stride(unsigned long long int stride)
     {
         discard_state_power2(stride);
     }
  
     __forceinline__ __device__ __host__ unsigned long long int operator()()
     {
         return this->next();
     }
  
     __forceinline__ __device__ __host__ unsigned long long int next()
     {
         unsigned long long int p = m_state.d;
         discard_state();
         return p;
     }
  
     __forceinline__ __device__ __host__ unsigned long long int current() const
     {
         return m_state.d;
     }
  
     __forceinline__ __device__ __host__ static constexpr bool uses_shared_vectors()
     {
         return UseSharedVectors;
     }
  
 protected:
     // Advances the internal state by offset times.
     __forceinline__ __device__ __host__ 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
     __forceinline__ __device__ __host__ void discard_state()
     {
         m_state.d ^= m_state.vectors[rightmost_zero_bit(m_state.i)];
         m_state.i++;
     }
  
     __forceinline__ __device__ __host__ 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
     __forceinline__ __device__ __host__ 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;
  
 __forceinline__ __device__ __host__ void rocrand_init(const unsigned long long int* vectors,
                                                       const unsigned int            offset,
                                                       rocrand_state_sobol64*        state)
 {
     *state = rocrand_state_sobol64(vectors, offset);
 }
  
 __forceinline__ __device__ __host__ unsigned long long int rocrand(rocrand_state_sobol64* state)
 {
     return state->next();
 }
  
 __forceinline__ __device__ __host__ void skipahead(unsigned long long int offset,
                                                    rocrand_state_sobol64* state)
 {
     return state->discard(offset);
 }
  // end of group rocranddevice
  
 #endif // ROCRAND_sobol64_H_