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 // SPDX-License-Identifier: MIT
 // Copyright (c) 2018-2025, Advanced Micro Devices, Inc. All rights reserved.
  
 #pragma once
  
 #include "ck_tile/core/config.hpp"
  
 namespace ck_tile {
  
 // Reference: https://github.com/Dao-AILab/flash-attention/blob/main/csrc/flash_attn/src/philox.cuh
 class philox
 {
     public:
     CK_TILE_HOST_DEVICE philox(unsigned long long seed_, unsigned long long offset_)
         : seed(reinterpret_cast<const uint2&>(seed_))
     {
  
         ull2* tmp = reinterpret_cast<ull2*>(&counter);
         tmp->x    = offset_;
     }
  
     CK_TILE_HOST_DEVICE uint4 get_philox_4x32(const unsigned long long subsequence) const
     {
  
         uint4 counter_ = counter;
         ull2* tmp      = reinterpret_cast<ull2*>(&counter_);
         tmp->y         = subsequence;
  
         uint2 key_ = seed;
 // 7-round philox
 #pragma unroll
         for(int i = 0; i < 6; i++)
         {
             counter_ = philox_single_round(counter_, key_);
             key_.x += kPhilox10A;
             key_.y += kPhilox10B;
         }
         uint4 output = philox_single_round(counter_, key_);
         return output;
     }
  
     CK_TILE_HOST_DEVICE void get_random_16x8(uint8_t* out,
                                              const unsigned long long subsequence) const
     {
         uint4 tmp_ph;
         tmp_ph = get_philox_4x32(subsequence);
  
         uint32_t* out_tmp = reinterpret_cast<uint32_t*>(&out[0]);
  
         out_tmp[0] = tmp_ph.x;
         out_tmp[1] = tmp_ph.y;
         out_tmp[2] = tmp_ph.z;
         out_tmp[3] = tmp_ph.w;
     }
  
     CK_TILE_HOST_DEVICE void get_random_8x8(uint8_t* out,
                                             const unsigned long long subsequence,
                                             const index_t idx0,
                                             const index_t idx1) const
     {
         uint4 tmp_ph;
         tmp_ph = get_philox_4x32(subsequence);
  
         uint32x4_t tmp;
         tmp[0]            = tmp_ph.x;
         tmp[1]            = tmp_ph.y;
         tmp[2]            = tmp_ph.z;
         tmp[3]            = tmp_ph.w;
         uint32_t* out_tmp = reinterpret_cast<uint32_t*>(&out[0]);
         out_tmp[0]        = tmp[idx0];
         out_tmp[1]        = tmp[idx1];
     }
  
     CK_TILE_HOST_DEVICE void
     get_random_4x8(uint8_t* out, const unsigned long long subsequence, const index_t idx) const
     {
         uint4 tmp_ph;
         tmp_ph = get_philox_4x32(subsequence);
  
         uint32x4_t tmp;
         tmp[0]            = tmp_ph.x;
         tmp[1]            = tmp_ph.y;
         tmp[2]            = tmp_ph.z;
         tmp[3]            = tmp_ph.w;
         uint32_t* out_tmp = reinterpret_cast<uint32_t*>(&out[0]);
         out_tmp[0]        = tmp[idx];
     }
  
     private:
     struct ull2
     {
         uint64_t x;
         uint64_t y;
     };
     uint4 counter;
     const uint2 seed;
  
     CK_TILE_HOST_DEVICE uint2 mulhilo32(const unsigned int a, const unsigned int b) const
     {
         uint2* res;
         unsigned long long tmp;
         tmp = static_cast<unsigned long long>(a) * b;
         res = reinterpret_cast<uint2*>(&tmp);
         return *res;
     }
  
     CK_TILE_HOST_DEVICE uint4 philox_single_round(const uint4 ctr, const uint2 key) const
     {
  
         uint2 res0 = mulhilo32(kPhiloxSA, ctr.x);
         uint2 res1 = mulhilo32(kPhiloxSB, ctr.z);
         uint4 ret  = {res1.y ^ ctr.y ^ key.x, res1.x, res0.y ^ ctr.w ^ key.y, res0.x};
         return ret;
     }
  
     static const unsigned long kPhilox10A = 0x9E3779B9;
     static const unsigned long kPhilox10B = 0xBB67AE85;
     static const unsigned long kPhiloxSA  = 0xD2511F53;
     static const unsigned long kPhiloxSB  = 0xCD9E8D57;
 };
  
 } // namespace ck_tile