Codechange: Replace GroupStatistics' num_engines with std::map. (#11849)

This removes manual memory management with calloc/free calls, and prevents potentially large arrays being allocated for each group.

(cherry picked from commit 8797cc7ef2)

src/build_vehicle_gui.cpp

@@ -252,7 +252,7 @@ static bool EngineIntroDateSorter(const GUIEngineListItem &a, const GUIEngineLis
 static bool EngineVehicleCountSorter(const GUIEngineListItem &a, const GUIEngineListItem &b)
 {
 	const GroupStatistics &stats = GroupStatistics::Get(_local_company, ALL_GROUP, Engine::Get(a.engine_id)->type);
-	const int r = ((int) stats.num_engines[a.engine_id]) - ((int) stats.num_engines[b.engine_id]);
+	const int r = ((int) stats.GetNumEngines(a.engine_id)) - ((int) stats.GetNumEngines(b.engine_id));
 
 	/* Use EngineID to sort instead since we want consistent sorting */
 	if (r == 0) return EngineNumberSorter(a, b);

src/group.h

@@ -16,6 +16,7 @@
 #include "vehicle_type.h"
 #include "engine_type.h"
 #include "livery.h"
+#include "3rdparty/cpp-btree/btree_map.h"
 #include <string>
 
 typedef Pool<Group, GroupID, 16, 64000> GroupPool;
@@ -25,15 +26,12 @@ extern GroupPool _group_pool; ///< Pool of groups.
 struct GroupStatistics {
 	Money profit_last_year;                 ///< Sum of profits for all vehicles.
 	Money profit_last_year_min_age;         ///< Sum of profits for vehicles considered for profit statistics.
-	uint16_t *num_engines;                  ///< Caches the number of engines of each type the company owns.
+	btree::btree_map<EngineID, uint16_t> num_engines; ///< Caches the number of engines of each type the company owns.
 	uint16_t num_vehicle;                   ///< Number of vehicles.
 	uint16_t num_vehicle_min_age;           ///< Number of vehicles considered for profit statistics;
 	bool autoreplace_defined;               ///< Are any autoreplace rules set?
 	bool autoreplace_finished;              ///< Have all autoreplacement finished?
 
-	GroupStatistics();
-	~GroupStatistics();
-
 	void Clear();
 
 	void ClearProfits()
@@ -50,6 +48,8 @@ struct GroupStatistics {
 		this->autoreplace_finished = false;
 	}
 
+	uint16_t GetNumEngines(EngineID engine) const;
+
 	static GroupStatistics &Get(CompanyID company, GroupID id_g, VehicleType type);
 	static GroupStatistics &Get(const Vehicle *v);
 	static GroupStatistics &GetAllGroup(const Vehicle *v);

src/group_cmd.cpp

@@ -35,16 +35,6 @@ GroupID _new_group_id;
 GroupPool _group_pool("Group");
 INSTANTIATE_POOL_METHODS(Group)
 
-GroupStatistics::GroupStatistics()
-{
-	this->num_engines = CallocT<uint16_t>(Engine::GetPoolSize());
-}
-
-GroupStatistics::~GroupStatistics()
-{
-	free(this->num_engines);
-}
-
 /**
  * Clear all caches.
  */
@@ -55,9 +45,20 @@ void GroupStatistics::Clear()
 	this->num_vehicle_min_age = 0;
 	this->profit_last_year_min_age = 0;
 
-	/* This is also called when NewGRF change. So the number of engines might have changed. Reallocate. */
-	free(this->num_engines);
-	this->num_engines = CallocT<uint16_t>(Engine::GetPoolSize());
+	/* This is also called when NewGRF change. So the number of engines might have changed. Reset. */
+	this->num_engines.clear();
+}
+
+/**
+ * Get number of vehicles of a specific engine ID.
+ * @param engine Engine ID.
+ * @returns number of vehicles of this engine ID.
+ */
+uint16_t GroupStatistics::GetNumEngines(EngineID engine) const
+{
+	auto found = this->num_engines.find(engine);
+	if (found != std::end(this->num_engines)) return found->second;
+	return 0;
 }
 
 /**
@@ -1032,9 +1033,9 @@ uint GetGroupNumEngines(CompanyID company, GroupID id_g, EngineID id_e)
 	uint count = 0;
 	const Engine *e = Engine::Get(id_e);
 	IterateDescendantsOfGroup(id_g, [&](Group *g) {
-		count += GroupStatistics::Get(company, g->index, e->type).num_engines[id_e];
+		count += GroupStatistics::Get(company, g->index, e->type).GetNumEngines(id_e);
 	});
-	return count + GroupStatistics::Get(company, id_g, e->type).num_engines[id_e];
+	return count + GroupStatistics::Get(company, id_g, e->type).GetNumEngines(id_e);
 }
 
 /**

src/script/api/script_engine.cpp

@@ -30,7 +30,7 @@
 	/* AIs have only access to engines they can purchase or still have in use.
 	 * Deity has access to all engined that will be or were available ever. */
 	CompanyID company = ScriptObject::GetCompany();
-	return ScriptCompanyMode::IsDeity() || ::IsEngineBuildable(engine_id, e->type, company) || ::Company::Get(company)->group_all[e->type].num_engines[engine_id] > 0;
+	return ScriptCompanyMode::IsDeity() || ::IsEngineBuildable(engine_id, e->type, company) || ::Company::Get(company)->group_all[e->type].GetNumEngines(engine_id) > 0;
 }
 
 /* static */ bool ScriptEngine::IsBuildable(EngineID engine_id)