Codechange: Cache train curve speed limit can be stored in 16 bits.

Cache curve speed modifier and max curve speed are both 16 bit values so can be stored in 16 bit types instead of 32 bit types.

(cherry picked from commit 3fc7b3b9a0a4cc34ae45a75a89a799b665a7bb09)

src/sl/vehicle_sl.cpp

@@ -1268,7 +1268,6 @@ struct vehicle_venc {
 struct train_venc {
 	VehicleID id;
 	GroundVehicleCache gvcache;
-	int cached_curve_speed_mod;
 	uint8_t cached_tflags;
 	uint8_t cached_num_engines;
 	uint16_t cached_centre_mass;
@@ -1277,7 +1276,8 @@ struct train_venc {
 	uint16_t cached_uncapped_decel;
 	uint8_t cached_deceleration;
 	byte user_def_data;
-	int cached_max_curve_speed;
+	int16_t cached_curve_speed_mod;
+	uint16_t cached_max_curve_speed;
 };
 
 struct roadvehicle_venc {
@@ -1340,7 +1340,6 @@ void Save_VENC()
 		for (Train *t : Train::Iterate()) {
 			SlWriteUint32(t->index);
 			write_gv_cache(t->gcache);
-			SlWriteUint32(t->tcache.cached_curve_speed_mod);
 			SlWriteByte(t->tcache.cached_tflags);
 			SlWriteByte(t->tcache.cached_num_engines);
 			SlWriteUint16(t->tcache.cached_centre_mass);
@@ -1349,7 +1348,8 @@ void Save_VENC()
 			SlWriteUint16(t->tcache.cached_uncapped_decel);
 			SlWriteByte(t->tcache.cached_deceleration);
 			SlWriteByte(t->tcache.user_def_data);
-			SlWriteUint32(t->tcache.cached_max_curve_speed);
+			SlWriteUint16((uint16_t)t->tcache.cached_curve_speed_mod);
+			SlWriteUint16(t->tcache.cached_max_curve_speed);
 		}
 
 		/* road vehicle */
@@ -1403,7 +1403,6 @@ void Load_VENC()
 	for (train_venc &venc : _train_vencs) {
 		venc.id = SlReadUint32();
 		read_gv_cache(venc.gvcache);
-		venc.cached_curve_speed_mod = SlReadUint32();
 		venc.cached_tflags = SlReadByte();
 		venc.cached_num_engines = SlReadByte();
 		venc.cached_centre_mass = SlReadUint16();
@@ -1412,7 +1411,8 @@ void Load_VENC()
 		venc.cached_uncapped_decel = SlReadUint16();
 		venc.cached_deceleration = SlReadByte();
 		venc.user_def_data = SlReadByte();
-		venc.cached_max_curve_speed = SlReadUint32();
+		venc.cached_curve_speed_mod = (int16_t)SlReadUint16();
+		venc.cached_max_curve_speed = SlReadUint16();
 	}
 
 	_roadvehicle_vencs.resize(SlReadUint32());

src/train.h

@@ -110,11 +110,7 @@ struct TrainCache {
 	/* Cached wagon override spritegroup */
 	const struct SpriteGroup *cached_override;
 
-	/* cached max. speed / acceleration data */
-	int cached_max_curve_speed;     ///< max consist speed limited by curves
-
 	/* cached values, recalculated on load and each time a vehicle is added to/removed from the consist. */
-	int cached_curve_speed_mod;     ///< curve speed modifier of the entire train
 	TrainCacheFlags cached_tflags;  ///< train cached flags
 	uint8_t cached_num_engines;     ///< total number of engines, including rear ends of multiheaded engines
 	uint16_t cached_centre_mass;    ///< Cached position of the centre of mass, from the front
@@ -124,6 +120,9 @@ struct TrainCache {
 	uint8_t cached_deceleration;    ///< Cached deceleration for realistic braking lookahead purposes
 
 	byte user_def_data;             ///< Cached property 0x25. Can be set by Callback 0x36.
+
+	int16_t cached_curve_speed_mod; ///< curve speed modifier of the entire train
+	uint16_t cached_max_curve_speed; ///< max consist speed limited by curves
 };
 
 /**
@@ -184,7 +183,7 @@ struct Train final : public GroundVehicle<Train, VEH_TRAIN> {
 
 	void ReserveTrackUnderConsist() const;
 
-	int GetCurveSpeedLimit() const;
+	uint16_t GetCurveSpeedLimit() const;
 
 	void ConsistChanged(ConsistChangeFlags allowed_changes);
 
@@ -479,7 +478,7 @@ protected: // These functions should not be called outside acceleration code.
 	 * Returns the curve speed modifier of this vehicle.
 	 * @return Current curve speed modifier, in fixed-point binary representation with 8 fractional bits.
 	 */
-	inline int GetCurveSpeedModifier() const
+	inline int16_t GetCurveSpeedModifier() const
 	{
 		return GetVehicleProperty(this, PROP_TRAIN_CURVE_SPEED_MOD, RailVehInfo(this->engine_type)->curve_speed_mod, true);
 	}

src/train_cmd.cpp

@@ -262,7 +262,7 @@ void Train::ConsistChanged(ConsistChangeFlags allowed_changes)
 
 	bool train_can_tilt = true;
 	bool speed_varies_by_railtype = false;
-	int min_curve_speed_mod = INT_MAX;
+	int16_t min_curve_speed_mod = INT16_MAX;
 
 	for (Train *u = this; u != nullptr; u = u->Next()) {
 		const RailVehicleInfo *rvi_u = RailVehInfo(u->engine_type);
@@ -607,7 +607,7 @@ int GetTrainStopLocation(StationID station_id, TileIndex tile, Train *v, bool up
  * Computes train speed limit caused by curves
  * @return imposed speed limit
  */
-int Train::GetCurveSpeedLimit() const
+uint16_t Train::GetCurveSpeedLimit() const
 {
 	dbg_assert(this->First() == this);
 
@@ -674,7 +674,7 @@ int Train::GetCurveSpeedLimit() const
 		max_speed = Clamp(max_speed, 2, absolute_max_speed);
 	}
 
-	return max_speed;
+	return static_cast<uint16_t>(max_speed);
 }
 
 void AdvanceOrderIndex(const Vehicle *v, VehicleOrderID &index)