Consolidating AllocationSize implementation

cub/cub/agent/single_pass_scan_operators.cuh

@@ -540,6 +540,65 @@ struct tile_state_with_memory_order
     return tile_state.template LoadValid<Order>(tile_idx);
   }
 };
+
+_CCCL_HOST_DEVICE _CCCL_FORCEINLINE constexpr int num_tiles_to_num_tile_states(int num_tiles)
+{
+  return CUB_PTX_WARP_THREADS + num_tiles;
+}
+
+_CCCL_HOST_DEVICE _CCCL_FORCEINLINE size_t
+tile_state_allocation_size(int bytes_per_description, int bytes_per_payload, int num_tiles)
+{
+  // Specify storage allocation requirements
+  size_t allocation_sizes[3];
+
+  int num_tile_states = num_tiles_to_num_tile_states(num_tiles);
+
+  // bytes needed for tile status descriptors
+  allocation_sizes[0] = num_tile_states * bytes_per_description;
+
+  // bytes needed for partials
+  allocation_sizes[1] = num_tile_states * bytes_per_payload;
+
+  // bytes needed for inclusives
+  allocation_sizes[2] = num_tile_states * bytes_per_payload;
+
+  // Set the necessary size of the blob
+  size_t temp_storage_bytes = 0;
+  void* allocations[3]      = {};
+  AliasTemporaries(nullptr, temp_storage_bytes, allocations, allocation_sizes);
+
+  return temp_storage_bytes;
+};
+
+_CCCL_HOST_DEVICE _CCCL_FORCEINLINE cudaError_t tile_state_init(
+  int bytes_per_description,
+  int bytes_per_payload,
+  int num_tiles,
+  void* d_temp_storage,
+  size_t temp_storage_bytes,
+  void* (&allocations)[3])
+{
+  // Specify storage allocation requirements
+  size_t allocation_sizes[3];
+
+  int num_tile_states = num_tiles_to_num_tile_states(num_tiles);
+
+  // bytes needed for tile status descriptors
+  allocation_sizes[0] = num_tile_states * bytes_per_description;
+
+  // bytes needed for partials
+  allocation_sizes[1] = num_tile_states * bytes_per_payload;
+
+  // bytes needed for inclusives
+  allocation_sizes[2] = num_tile_states * bytes_per_payload;
+
+  // Set the necessary size of the blob
+  AliasTemporaries(d_temp_storage, temp_storage_bytes, allocations, allocation_sizes);
+
+  return cudaSuccess;
+}
+
 } // namespace detail
 
 /**
@@ -583,6 +642,9 @@ struct ScanTileState<T, true>
   // Device storage
   TxnWord* d_tile_descriptors;
 
+  static constexpr size_t description_bytes_per_tile = sizeof(TxnWord);
+  static constexpr size_t payload_bytes_per_tile     = 0;
+
   /// Constructor
   _CCCL_HOST_DEVICE _CCCL_FORCEINLINE ScanTileState()
       : d_tile_descriptors(nullptr)
@@ -618,10 +680,11 @@ struct ScanTileState<T, true>
    * @param[out] temp_storage_bytes
    *   Size in bytes of \t d_temp_storage allocation
    */
-  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE static cudaError_t AllocationSize(int num_tiles, size_t& temp_storage_bytes)
+  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE static constexpr cudaError_t
+  AllocationSize(int num_tiles, size_t& temp_storage_bytes)
   {
-    // bytes needed for tile status descriptors
-    temp_storage_bytes = (num_tiles + TILE_STATUS_PADDING) * sizeof(TxnWord);
+    temp_storage_bytes =
+      detail::tile_state_allocation_size(description_bytes_per_tile, payload_bytes_per_tile, num_tiles);
     return cudaSuccess;
   }
 
@@ -782,6 +845,9 @@ struct ScanTileState<T, false>
   T* d_tile_partial;
   T* d_tile_inclusive;
 
+  static constexpr size_t description_bytes_per_tile = sizeof(StatusWord);
+  static constexpr size_t payload_bytes_per_tile     = sizeof(Uninitialized<T>);
+
   /// Constructor
   _CCCL_HOST_DEVICE _CCCL_FORCEINLINE ScanTileState()
       : d_tile_status(nullptr)
@@ -847,25 +913,13 @@ struct ScanTileState<T, false>
    * @param[out] temp_storage_bytes
    *   Size in bytes of \t d_temp_storage allocation
    */
-  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE static cudaError_t AllocationSize(int num_tiles, size_t& temp_storage_bytes)
+  _CCCL_HOST_DEVICE _CCCL_FORCEINLINE static constexpr cudaError_t
+  AllocationSize(int num_tiles, size_t& temp_storage_bytes)
   {
-    // Specify storage allocation requirements
-    size_t allocation_sizes[3];
-
-    // bytes needed for tile status descriptors
-    allocation_sizes[0] = (num_tiles + TILE_STATUS_PADDING) * sizeof(StatusWord);
-
-    // bytes needed for partials
-    allocation_sizes[1] = (num_tiles + TILE_STATUS_PADDING) * sizeof(Uninitialized<T>);
-
-    // bytes needed for inclusives
-    allocation_sizes[2] = (num_tiles + TILE_STATUS_PADDING) * sizeof(Uninitialized<T>);
-
-    // Set the necessary size of the blob
-    void* allocations[3] = {};
-    return CubDebug(AliasTemporaries(nullptr, temp_storage_bytes, allocations, allocation_sizes));
+    temp_storage_bytes =
+      detail::tile_state_allocation_size(description_bytes_per_tile, payload_bytes_per_tile, num_tiles);
+    return cudaSuccess;
   }
-
   /**
    * Initialize (from device)
    */