[vpr][place][net_cost] add get_chanz_cost_factor signiture and acc_tile_num_inter_die_conn_

Author: amin1377

vpr/src/place/net_cost_handler.h

@@ -196,12 +196,12 @@ class NetCostHandler {
     vtr::NdOffsetMatrix<float, 2> chanx_place_cost_fac_; // [-1...device_ctx.grid.width()-1]
     vtr::NdOffsetMatrix<float, 2> chany_place_cost_fac_; // [-1...device_ctx.grid.height()-1]
     /**
-      @brief This data structure functions similarly to the matrices described above 
-      but is applied to 3D connections linking different FPGA layers. It is used in the 
-      placement cost function calculation, where the height of the bounding box is divided 
-      by the average number of inter-die connections within the bounding box.
+      @brief This data structure stores the cumulative number of inter-die connections from the lower-left corner. 
+      * It is later used to calculate the chanZ factor, which functions similarly to chanx_place_cost_fac_ and chany_place_cost_fac_, 
+      * but applies to the height of the bounding box. The chanZ factor is calculated during block placement because storing it in the 
+      * same way as the X and Y cost factors would require a 4D array and population it is an O(n^2) operation.
      */
-    vtr::NdMatrix<float, 4> chanz_place_cost_fac_; // [0...device_ctx.grid.width()-1][0...device_ctx.grid.height()-1][0...device_ctx.grid.width()-1][0...device_ctx.grid.height()-1]
+    vtr::NdMatrix<float, 2> acc_tile_num_inter_die_conn_;
 
 
   private:
@@ -511,4 +511,14 @@ class NetCostHandler {
      */
     double get_net_wirelength_from_layer_bb_(ClusterNetId net_id);
 
+    /**
+     * @brief Calculate the chanz cost factor based on the inverse of the average number of inter-die connections 
+     * in the given bounding box. This cost factor increases the placement cost for blocks that require inter-layer 
+     * connections in areas with, on average, fewer inter-die connections. If inter-die connections are evenly 
+     * distributed across tiles, the cost factor will be the same for all bounding boxes.
+     * @param bounding_box Bounding box of the net which chanz cost factor is to be calculated
+     * @return ChanZ cost factor
+     */
+    float get_chanz_cost_factor(const t_bb& bounding_box);
+
 };