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authorrubidium <rubidium@openttd.org>2014-07-22 19:46:10 +0000
committerrubidium <rubidium@openttd.org>2014-07-22 19:46:10 +0000
commitf3d085e33c00d53ba8b16b45c5aec888bfb7b50c (patch)
treeca283f910ef0d043dafdada881b8ae6074130c0b
parenta96a57e1619ff2cfc3f40508fca8418807669c7b (diff)
downloadopenttd-f3d085e33c00d53ba8b16b45c5aec888bfb7b50c.tar.xz
(svn r26702) -Fix [FS#6067]: integer overflows in acceleration code causing either too low acceleration or too large acceleration
-rw-r--r--src/ground_vehicle.cpp33
-rw-r--r--src/ground_vehicle.hpp4
2 files changed, 27 insertions, 10 deletions
diff --git a/src/ground_vehicle.cpp b/src/ground_vehicle.cpp
index f3134608a..fcdab77b0 100644
--- a/src/ground_vehicle.cpp
+++ b/src/ground_vehicle.cpp
@@ -108,15 +108,30 @@ int GroundVehicle<T, Type>::GetAcceleration() const
{
/* Templated class used for function calls for performance reasons. */
const T *v = T::From(this);
- int32 speed = v->GetCurrentSpeed(); // [km/h-ish]
+ /* Speed is used squared later on, so U16 * U16, and then multiplied by other values. */
+ int64 speed = v->GetCurrentSpeed(); // [km/h-ish]
/* Weight is stored in tonnes. */
int32 mass = this->gcache.cached_weight;
- /* Power is stored in HP, we need it in watts. */
- int32 power = this->gcache.cached_power * 746;
-
- int32 resistance = 0;
+ /* Power is stored in HP, we need it in watts.
+ * Each vehicle can have U16 power, 128 vehicles, HP -> watt
+ * and km/h to m/s conversion below result in a maxium of
+ * about 1.1E11, way more than 4.3E9 of int32. */
+ int64 power = this->gcache.cached_power * 746ll;
+
+ /* This is constructed from:
+ * - axle resistance: U16 power * 10 for 128 vehicles.
+ * * 8.3E7
+ * - rolling friction: U16 power * 144 for 128 vehicles.
+ * * 1.2E9
+ * - slope resistance: U16 weight * 100 * 10 (steepness) for 128 vehicles.
+ * * 8.4E9
+ * - air drag: 28 * (U8 drag + 3 * U8 drag * 128 vehicles / 20) * U16 speed * U16 speed
+ * * 6.2E14 before dividing by 1000
+ * Sum is 6.3E11, more than 4.3E9 of int32, so int64 is needed.
+ */
+ int64 resistance = 0;
bool maglev = v->GetAccelerationType() == 2;
@@ -136,7 +151,9 @@ int GroundVehicle<T, Type>::GetAcceleration() const
AccelStatus mode = v->GetAccelerationStatus();
const int max_te = this->gcache.cached_max_te; // [N]
- int force;
+ /* Constructued from power, with need to multiply by 18 and assuming
+ * low speed, it needs to be a 64 bit integer too. */
+ int64 force;
if (speed > 0) {
if (!maglev) {
/* Conversion factor from km/h to m/s is 5/18 to get [N] in the end. */
@@ -160,10 +177,10 @@ int GroundVehicle<T, Type>::GetAcceleration() const
* down hill will never slow down enough, and a vehicle that came up
* a hill will never speed up enough to (eventually) get back to the
* same (maximum) speed. */
- int accel = (force - resistance) / (mass * 4);
+ int accel = ClampToI32((force - resistance) / (mass * 4));
return force < resistance ? min(-1, accel) : max(1, accel);
} else {
- return min(-force - resistance, -10000) / mass;
+ return ClampToI32(min(-force - resistance, -10000) / mass);
}
}
diff --git a/src/ground_vehicle.hpp b/src/ground_vehicle.hpp
index 80a88b705..c38c6c4b7 100644
--- a/src/ground_vehicle.hpp
+++ b/src/ground_vehicle.hpp
@@ -113,9 +113,9 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
* Calculates the total slope resistance for this vehicle.
* @return Slope resistance.
*/
- inline int32 GetSlopeResistance() const
+ inline int64 GetSlopeResistance() const
{
- int32 incl = 0;
+ int64 incl = 0;
for (const T *u = T::From(this); u != NULL; u = u->Next()) {
if (HasBit(u->gv_flags, GVF_GOINGUP_BIT)) {