[APPack] Added Max Displacement Metric

Added the ability to print the max displacement from the placement
reconstruction to the original flat placement.

This metric will help show another dimension to the flat placement
reconstruction. Generally, if the average displacement is low, that may
not be good if that means that one atom is placed way farther away than
where it would like. This can really hurt quality.

Turned the distance calculation into the Manhattan Norm instead of the
Euclidean Norm.

Author: AlexandreSinger

vpr/src/base/load_flat_place.cpp

@@ -8,6 +8,7 @@
 
 #include "load_flat_place.h"
 
+#include <algorithm>
 #include <fstream>
 #include <unordered_set>
 #include "atom_lookup.h"
@@ -254,7 +255,8 @@ void log_flat_placement_reconstruction_info(
     // Go through each atom and compute how much it has displaced and count
     // how many have been displaced beyond some threshold.
     constexpr float disp_threashold = 0.5f;
-    float total_disp = 0;
+    float total_disp = 0.f;
+    float max_disp = 0.f;
     unsigned num_atoms_missplaced = 0;
     for (AtomBlockId atom_blk_id : atom_netlist.blocks()) {
         // TODO: Currently only handle the case when all of the position
@@ -279,7 +281,11 @@ void log_flat_placement_reconstruction_info(
         float dx = blk_x - clb_loc.loc.x;
         float dy = blk_y - clb_loc.loc.y;
         float dlayer = blk_layer - clb_loc.loc.layer;
-        float dist = std::sqrt((dx * dx) + (dy * dy) + (dlayer * dlayer));
+        // Using the Manhattan distance (L1 norm)
+        float dist = std::abs(dx) + std::abs(dy) + std::abs(dlayer);
+
+        // Collect the max displacement.
+        max_disp = std::max(max_disp, dist);
 
         // Accumulate into the total displacement.
         total_disp += dist;
@@ -311,6 +317,8 @@ void log_flat_placement_reconstruction_info(
             total_disp);
     VTR_LOG("\tAverage atom displacement of initial placement from flat placement: %f\n",
             total_disp / static_cast<float>(num_atoms));
+    VTR_LOG("\tMax atom displacement of initial placement from flat placement: %f\n",
+            max_disp);
     VTR_LOG("\tPercent of atoms misplaced from the flat placement: %f\n",
             static_cast<float>(num_atoms_missplaced) / static_cast<float>(num_atoms));
 }