Coalesce neighboring symbol maps for better lookup performance

kitty/fonts/render.py

@@ -25,8 +25,29 @@ else:
 current_faces = None
 
 
+def coalesce_symbol_maps(maps):
+    if not maps:
+        return maps
+    items = tuple((k, maps[k]) for k in sorted(maps))
+    ans = [items[0]]
+
+    def merge(prev_item, item):
+        s, e = item[0]
+        pe = prev_item[0][1]
+        ans[-1] = ((prev_item[0][0], max(pe, e)), prev_item[1])
+
+    for item in items[1:]:
+        current_item = ans[-1]
+        if current_item[1] != item[1] or item[0][0] > current_item[0][1] + 1:
+            ans.append(item)
+        else:
+            merge(current_item, item)
+
+    return dict(ans)
+
+
 def create_symbol_map(opts):
-    val = opts.symbol_map
+    val = coalesce_symbol_maps(opts.symbol_map)
     family_map = {}
     count = 0
     for family in val.values():