# HG changeset patch
# User Peter Nelson <peter1138@openttd.org>
# Date 2024-02-25 12:36:13
# Node ID c7d0936f4cf0e778b7456281a406653b26f51215
# Parent  dd35d3d734acfbd792f7d6a1b7a979c11623a6c5

Change: Use bitmap for free unit ID generation. (#12165)

This improves performance of finding the next free unit number for a vehicle.

Based loosely on pool's used slot bitmap.

diff --git a/src/company_base.h b/src/company_base.h
--- a/src/company_base.h
+++ b/src/company_base.h
@@ -49,6 +49,19 @@ struct CompanyInfrastructure {
 	uint32_t GetTramTotal() const;
 };
 
+class FreeUnitIDGenerator {
+public:
+	UnitID NextID() const;
+	UnitID UseID(UnitID index);
+	void ReleaseID(UnitID index);
+
+private:
+	using BitmapStorage = size_t;
+	static constexpr size_t BITMAP_SIZE = std::numeric_limits<BitmapStorage>::digits;
+
+	std::vector<BitmapStorage> used_bitmap;
+};
+
 typedef Pool<Company, CompanyID, 1, MAX_COMPANIES> CompanyPool;
 extern CompanyPool _company_pool;
 
@@ -129,6 +142,8 @@ struct Company : CompanyProperties, Comp
 
 	CompanyInfrastructure infrastructure; ///< NOSAVE: Counts of company owned infrastructure.
 
+	FreeUnitIDGenerator freeunits[VEH_COMPANY_END];
+
 	Money GetMaxLoan() const;
 
 	/**
diff --git a/src/economy.cpp b/src/economy.cpp
--- a/src/economy.cpp
+++ b/src/economy.cpp
@@ -430,17 +430,13 @@ void ChangeOwnershipOfCompanyItems(Owner
 	}
 
 	{
-		FreeUnitIDGenerator unitidgen[] = {
-			FreeUnitIDGenerator(VEH_TRAIN, new_owner), FreeUnitIDGenerator(VEH_ROAD,     new_owner),
-			FreeUnitIDGenerator(VEH_SHIP,  new_owner), FreeUnitIDGenerator(VEH_AIRCRAFT, new_owner)
-		};
+		Company *new_company = new_owner == INVALID_OWNER ? nullptr : Company::Get(new_owner);
 
 		/* Override company settings to new company defaults in case we need to convert them.
 		 * This is required as the CmdChangeServiceInt doesn't copy the supplied value when it is non-custom
 		 */
 		if (new_owner != INVALID_OWNER) {
 			Company *old_company = Company::Get(old_owner);
-			Company *new_company = Company::Get(new_owner);
 
 			old_company->settings.vehicle.servint_aircraft = new_company->settings.vehicle.servint_aircraft;
 			old_company->settings.vehicle.servint_trains = new_company->settings.vehicle.servint_trains;
@@ -457,8 +453,6 @@ void ChangeOwnershipOfCompanyItems(Owner
 				 * This prevents invalid values on mismatching company defaults being accepted.
 				 */
 				if (!v->ServiceIntervalIsCustom()) {
-					Company *new_company = Company::Get(new_owner);
-
 					/* Technically, passing the interval is not needed as the command will query the default value itself.
 					 * However, do not rely on that behaviour.
 					 */
@@ -477,7 +471,8 @@ void ChangeOwnershipOfCompanyItems(Owner
 				}
 				if (v->IsPrimaryVehicle()) {
 					GroupStatistics::CountVehicle(v, 1);
-					v->unitnumber = unitidgen[v->type].NextID();
+					auto &unitidgen = new_company->freeunits[v->type];
+					v->unitnumber = unitidgen.UseID(unitidgen.NextID());
 				}
 
 				/* Invalidate the vehicle's cargo payment "owner cache". */
diff --git a/src/saveload/vehicle_sl.cpp b/src/saveload/vehicle_sl.cpp
--- a/src/saveload/vehicle_sl.cpp
+++ b/src/saveload/vehicle_sl.cpp
@@ -517,6 +517,10 @@ void AfterLoadVehicles(bool part_of_load
 			default: break;
 		}
 
+		if (part_of_load && v->unitnumber != 0) {
+			Company::Get(v->owner)->freeunits[v->type].UseID(v->unitnumber);
+		}
+
 		v->UpdateDeltaXY();
 		v->coord.left = INVALID_COORD;
 		v->sprite_cache.old_coord.left = INVALID_COORD;
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -1178,7 +1178,7 @@ static void NormaliseTrainHead(Train *he
 
 	/* If we don't have a unit number yet, set one. */
 	if (head->unitnumber != 0) return;
-	head->unitnumber = GetFreeUnitNumber(VEH_TRAIN);
+	head->unitnumber = Company::Get(head->owner)->freeunits[head->type].UseID(GetFreeUnitNumber(VEH_TRAIN));
 }
 
 /**
@@ -1336,6 +1336,7 @@ CommandCost CmdMoveRailVehicle(DoCommand
 			}
 			/* Remove stuff not valid anymore for non-front engines. */
 			DeleteVehicleOrders(src);
+			Company::Get(src->owner)->freeunits[src->type].ReleaseID(src->unitnumber);
 			src->unitnumber = 0;
 			src->name.clear();
 		}
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -846,6 +846,8 @@ void Vehicle::PreDestructor()
 		DeleteGroupHighlightOfVehicle(this);
 	}
 
+	Company::Get(this->owner)->freeunits[this->type].ReleaseID(this->unitnumber);
+
 	if (this->type == VEH_AIRCRAFT && this->IsPrimaryVehicle()) {
 		Aircraft *a = Aircraft::From(this);
 		Station *st = GetTargetAirportIfValid(a);
@@ -1816,44 +1818,50 @@ VehicleEnterTileStatus VehicleEnterTile(
 }
 
 /**
- * Initializes the structure. Vehicle unit numbers are supposed not to change after
- * struct initialization, except after each call to this->NextID() the returned value
- * is assigned to a vehicle.
- * @param type type of vehicle
- * @param owner owner of vehicles
+ * Find first unused unit number.
+ * This does not mark the unit number as used.
+ * @returns First unused unit number.
  */
-FreeUnitIDGenerator::FreeUnitIDGenerator(VehicleType type, CompanyID owner) : cache(nullptr), maxid(0), curid(0)
+UnitID FreeUnitIDGenerator::NextID() const
 {
-	/* Find maximum */
-	for (const Vehicle *v : Vehicle::Iterate()) {
-		if (v->type == type && v->owner == owner) {
-			this->maxid = std::max<UnitID>(this->maxid, v->unitnumber);
-		}
+	for (auto it = std::begin(this->used_bitmap); it != std::end(this->used_bitmap); ++it) {
+		BitmapStorage available = ~(*it);
+		if (available == 0) continue;
+		return static_cast<UnitID>(std::distance(std::begin(this->used_bitmap), it) * BITMAP_SIZE + FindFirstBit(available) + 1);
 	}
-
-	if (this->maxid == 0) return;
-
-	/* Reserving 'maxid + 2' because we need:
-	 * - space for the last item (with v->unitnumber == maxid)
-	 * - one free slot working as loop terminator in FreeUnitIDGenerator::NextID() */
-	this->cache = CallocT<bool>(this->maxid + 2);
-
-	/* Fill the cache */
-	for (const Vehicle *v : Vehicle::Iterate()) {
-		if (v->type == type && v->owner == owner) {
-			this->cache[v->unitnumber] = true;
-		}
-	}
+	return static_cast<UnitID>(this->used_bitmap.size() * BITMAP_SIZE + 1);
 }
 
-/** Returns next free UnitID. Supposes the last returned value was assigned to a vehicle. */
-UnitID FreeUnitIDGenerator::NextID()
+/**
+ * Use a unit number. If the unit number is not valid it is ignored.
+ * @param index Unit number to use.
+ * @returns Unit number used.
+ */
+UnitID FreeUnitIDGenerator::UseID(UnitID index)
 {
-	if (this->maxid <= this->curid) return ++this->curid;
-
-	while (this->cache[++this->curid]) { } // it will stop, we reserved more space than needed
-
-	return this->curid;
+	if (index == 0 || index == UINT16_MAX) return index;
+
+	index--;
+
+	size_t slot = index / BITMAP_SIZE;
+	if (slot >= this->used_bitmap.size()) this->used_bitmap.resize(slot + 1);
+	SetBit(this->used_bitmap[index / BITMAP_SIZE], index % BITMAP_SIZE);
+
+	return index + 1;
+}
+
+/**
+ * Release a unit number. If the unit number is not valid it is ignored.
+ * @param index Unit number to release.
+ */
+void FreeUnitIDGenerator::ReleaseID(UnitID index)
+{
+	if (index == 0 || index == UINT16_MAX) return;
+
+	index--;
+
+	assert(index / BITMAP_SIZE < this->used_bitmap.size());
+	ClrBit(this->used_bitmap[index / BITMAP_SIZE], index % BITMAP_SIZE);
 }
 
 /**
@@ -1876,9 +1884,7 @@ UnitID GetFreeUnitNumber(VehicleType typ
 	const Company *c = Company::Get(_current_company);
 	if (c->group_all[type].num_vehicle >= max_veh) return UINT16_MAX; // Currently already at the limit, no room to make a new one.
 
-	FreeUnitIDGenerator gen(type, _current_company);
-
-	return gen.NextID();
+	return c->freeunits[type].NextID();
 }
 
 
diff --git a/src/vehicle_base.h b/src/vehicle_base.h
--- a/src/vehicle_base.h
+++ b/src/vehicle_base.h
@@ -755,7 +755,7 @@ public:
 	 * and that shall not be resetted for the new vehicle.
 	 * @param src The old vehicle
 	 */
-	inline void CopyVehicleConfigAndStatistics(const Vehicle *src)
+	inline void CopyVehicleConfigAndStatistics(Vehicle *src)
 	{
 		this->CopyConsistPropertiesFrom(src);
 
@@ -766,6 +766,8 @@ public:
 
 		this->profit_this_year = src->profit_this_year;
 		this->profit_last_year = src->profit_last_year;
+
+		src->unitnumber = 0;
 	}
 
 
@@ -1270,19 +1272,6 @@ struct SpecializedVehicle : public Vehic
 	static Pool::IterateWrapper<T> Iterate(size_t from = 0) { return Pool::IterateWrapper<T>(from); }
 };
 
-/** Generates sequence of free UnitID numbers */
-struct FreeUnitIDGenerator {
-	bool *cache;  ///< array of occupied unit id numbers
-	UnitID maxid; ///< maximum ID at the moment of constructor call
-	UnitID curid; ///< last ID returned; 0 if none
-
-	FreeUnitIDGenerator(VehicleType type, CompanyID owner);
-	UnitID NextID();
-
-	/** Releases allocated memory */
-	~FreeUnitIDGenerator() { free(this->cache); }
-};
-
 /** Sentinel for an invalid coordinate. */
 static const int32_t INVALID_COORD = 0x7fffffff;
 
diff --git a/src/vehicle_cmd.cpp b/src/vehicle_cmd.cpp
--- a/src/vehicle_cmd.cpp
+++ b/src/vehicle_cmd.cpp
@@ -194,6 +194,8 @@ std::tuple<CommandCost, VehicleID, uint,
 				GroupStatistics::CountVehicle(v, 1);
 				if (!(subflags & DC_AUTOREPLACE)) OrderBackup::Restore(v, client_id);
 			}
+
+			Company::Get(v->owner)->freeunits[v->type].UseID(v->unitnumber);
 		}