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   * Copyright (c) 2011, Duane Merrill.  All rights reserved.
   * Copyright (c) 2011-2018, NVIDIA CORPORATION.  All rights reserved.
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  /**
   * \file
   * cub::GridEvenShare is a descriptor utility for distributing input among CUDA thread blocks in an "even-share" fashion.  Each thread block gets roughly the same number of fixed-size work units (grains).
   */
  
  
  #pragma once
  
  #include "../util_namespace.cuh"
  #include "../util_macro.cuh"
  #include "grid_mapping.cuh"
  
  /// Optional outer namespace(s)
  CUB_NS_PREFIX
  
  /// CUB namespace
  namespace cub {
  
  
  /**
   * \addtogroup GridModule
   * @{
   */
  
  
  /**
   * \brief GridEvenShare is a descriptor utility for distributing input among
   * CUDA thread blocks in an "even-share" fashion.  Each thread block gets roughly
   * the same number of input tiles.
   *
   * \par Overview
   * Each thread block is assigned a consecutive sequence of input tiles.  To help
   * preserve alignment and eliminate the overhead of guarded loads for all but the
   * last thread block, to GridEvenShare assigns one of three different amounts of
   * work to a given thread block: "big", "normal", or "last".  The "big" workloads
   * are one scheduling grain larger than "normal".  The "last" work unit for the
   * last thread block may be partially-full if the input is not an even multiple of
   * the scheduling grain size.
   *
   * \par
   * Before invoking a child grid, a parent thread will typically construct an
   * instance of GridEvenShare.  The instance can be passed to child thread blocks
   * which can initialize their per-thread block offsets using \p BlockInit().
   */
  template <typename OffsetT>
  struct GridEvenShare
  {
  private:
  
      OffsetT     total_tiles;
      int         big_shares;
      OffsetT     big_share_items;
      OffsetT     normal_share_items;
      OffsetT     normal_base_offset;
  
  public:
  
      /// Total number of input items
      OffsetT     num_items;
  
      /// Grid size in thread blocks
      int         grid_size;
  
      /// OffsetT into input marking the beginning of the owning thread block's segment of input tiles
      OffsetT     block_offset;
  
      /// OffsetT into input of marking the end (one-past) of the owning thread block's segment of input tiles
      OffsetT     block_end;
  
      /// Stride between input tiles
      OffsetT     block_stride;
  
  
      /**
       * \brief Constructor.
       */
      __host__ __device__ __forceinline__ GridEvenShare() :
          total_tiles(0),
          big_shares(0),
          big_share_items(0),
          normal_share_items(0),
          normal_base_offset(0),
          num_items(0),
          grid_size(0),
          block_offset(0),
          block_end(0),
          block_stride(0)
      {}
  
  
      /**
       * \brief Dispatch initializer. To be called prior prior to kernel launch.
       */
      __host__ __device__ __forceinline__ void DispatchInit(
          OffsetT num_items,          ///< Total number of input items
          int     max_grid_size,      ///< Maximum grid size allowable (actual grid size may be less if not warranted by the the number of input items)
          int     tile_items)         ///< Number of data items per input tile
      {
          this->block_offset          = num_items;    // Initialize past-the-end
          this->block_end             = num_items;    // Initialize past-the-end
          this->num_items             = num_items;
          this->total_tiles           = (num_items + tile_items - 1) / tile_items;
          this->grid_size             = CUB_MIN(total_tiles, max_grid_size);
          OffsetT avg_tiles_per_block = total_tiles / grid_size;
          this->big_shares            = total_tiles - (avg_tiles_per_block * grid_size);        // leftover grains go to big blocks
          this->normal_share_items    = avg_tiles_per_block * tile_items;
          this->normal_base_offset    = big_shares * tile_items;
          this->big_share_items       = normal_share_items + tile_items;
      }
  
  
      /**
       * \brief Initializes ranges for the specified thread block index.  Specialized
       * for a "raking" access pattern in which each thread block is assigned a
       * consecutive sequence of input tiles.
       */
      template <int TILE_ITEMS>
      __device__ __forceinline__ void BlockInit(
          int block_id,
          Int2Type<GRID_MAPPING_RAKE> /*strategy_tag*/)
      {
          block_stride = TILE_ITEMS;
          if (block_id < big_shares)
          {
              // This thread block gets a big share of grains (avg_tiles_per_block + 1)
              block_offset = (block_id * big_share_items);
              block_end = block_offset + big_share_items;
          }
          else if (block_id < total_tiles)
          {
              // This thread block gets a normal share of grains (avg_tiles_per_block)
              block_offset = normal_base_offset + (block_id * normal_share_items);
              block_end = CUB_MIN(num_items, block_offset + normal_share_items);
          }
          // Else default past-the-end
      }
  
  
      /**
       * \brief Block-initialization, specialized for a "raking" access
       * pattern in which each thread block is assigned a consecutive sequence
       * of input tiles.
       */
      template <int TILE_ITEMS>
      __device__ __forceinline__ void BlockInit(
          int block_id,
          Int2Type<GRID_MAPPING_STRIP_MINE> /*strategy_tag*/)
      {
          block_stride = grid_size * TILE_ITEMS;
          block_offset = (block_id * TILE_ITEMS);
          block_end = num_items;
      }
  
  
      /**
       * \brief Block-initialization, specialized for "strip mining" access
       * pattern in which the input tiles assigned to each thread block are
       * separated by a stride equal to the the extent of the grid.
       */
      template <
          int TILE_ITEMS,
          GridMappingStrategy STRATEGY>
      __device__ __forceinline__ void BlockInit()
      {
          BlockInit<TILE_ITEMS>(blockIdx.x, Int2Type<STRATEGY>());
      }
  
  
      /**
       * \brief Block-initialization, specialized for a "raking" access
       * pattern in which each thread block is assigned a consecutive sequence
       * of input tiles.
       */
      template <int TILE_ITEMS>
      __device__ __forceinline__ void BlockInit(
          OffsetT block_offset,                       ///< [in] Threadblock begin offset (inclusive)
          OffsetT block_end)                          ///< [in] Threadblock end offset (exclusive)
      {
          this->block_offset = block_offset;
          this->block_end = block_end;
          this->block_stride = TILE_ITEMS;
      }
  
  
  };
  
  
  
  
  
  /** @} */       // end group GridModule
  
  }               // CUB namespace
  CUB_NS_POSTFIX  // Optional outer namespace(s)