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(svn r21883) -Codechange: make UpdateZPosition() faster by not calling GetSlopeZ() when not needed

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smatz
2011-01-21 17:35:17 +00:00
parent e860075a16
commit 8b9f0d5ade
3 changed files with 103 additions and 6 deletions
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69
src/ground_vehicle.hpp
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@@ -148,16 +148,73 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
/**
* Updates vehicle's Z position.
* Inclination can't change in the middle of a tile.
* The faster code is used for trains and road vehicles unless they are
* reversing on a sloped tile.
*/
FORCEINLINE void UpdateZPosition()
{
/* Vehicle's Z position can change only if it has GVF_GOINGUP_BIT or GVF_GOINGDOWN_BIT set */
if (HasBit(this->gv_flags, GVF_GOINGUP_BIT) || HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
this->z_pos = GetSlopeZ(this->x_pos, this->y_pos);
} else {
/* Verify that assumption. */
assert(this->z_pos == GetSlopeZ(this->x_pos, this->y_pos));
#if 0
/* The following code does this: */
if (HasBit(this->gv_flags, GVF_GOINGUP_BIT)) {
switch (this->direction) {
case DIR_NE:
this->z_pos += (this->x_pos & 1); break;
case DIR_SW:
this->z_pos += (this->x_pos & 1) ^ 1; break;
case DIR_NW:
this->z_pos += (this->y_pos & 1); break;
case DIR_SE:
this->z_pos += (this->y_pos & 1) ^ 1; break;
default: break;
}
} else if (HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
switch (this->direction) {
case DIR_NE:
this->z_pos -= (this->x_pos & 1); break;
case DIR_SW:
this->z_pos -= (this->x_pos & 1) ^ 1; break;
case DIR_NW:
this->z_pos -= (this->y_pos & 1); break;
case DIR_SE:
this->z_pos -= (this->y_pos & 1) ^ 1; break;
default: break;
}
}
/* But gcc 4.4.5 isn't able to nicely optimise it, and the resulting
* code is full of conditional jumps. */
#endif
/* Vehicle's Z position can change only if it has GVF_GOINGUP_BIT or GVF_GOINGDOWN_BIT set.
* Furthermore, if this function is called once every time the vehicle's position changes,
* we know the Z position changes by +/-1 at certain moments - when x_pos, y_pos is odd/even,
* depending on orientation of the slope and vehicle's direction */
if (HasBit(this->gv_flags, GVF_GOINGUP_BIT) || HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
if (T::From(this)->HasToUseGetSlopeZ()) {
/* In some cases, we have to use GetSlopeZ() */
this->z_pos = GetSlopeZ(this->x_pos, this->y_pos);
return;
}
/* DirToDiagDir() is a simple right shift */
DiagDirection dir = DirToDiagDir(this->direction);
/* Read variables, so the compiler knows the access doesn't trap */
int8 x_pos = this->x_pos;
int8 y_pos = this->y_pos;
/* DiagDirToAxis() is a simple mask */
int8 d = DiagDirToAxis(dir) == AXIS_X ? x_pos : y_pos;
/* We need only the least significant bit */
d &= 1;
/* Conditional "^ 1". Optimised to "(dir - 1) <= 1". */
d ^= (int8)(dir == DIAGDIR_SW || dir == DIAGDIR_SE);
/* Subtraction instead of addition because we are testing for GVF_GOINGUP_BIT.
* GVF_GOINGUP_BIT is used because it's bit 0, so simple AND can be used,
* without any shift */
this->z_pos += HasBit(this->gv_flags, GVF_GOINGUP_BIT) ? d : -d;
}
assert(this->z_pos == GetSlopeZ(this->x_pos, this->y_pos));
}
/**