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(svn r26702) -Fix [FS#6067]: integer overflows in acceleration code causing either too low acceleration or too large acceleration

This commit is contained in:
rubidium 2014-07-22 19:46:10 +00:00
parent a96a57e161
commit f3d085e33c
2 changed files with 26 additions and 9 deletions
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31
src/ground_vehicle.cpp
View File

@ -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;
/* 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;
int32 resistance = 0;
/* 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);
}
}

4
src/ground_vehicle.hpp
View File

@ -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)) {