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(svn r16641) -Codechange: reduce number of multiplications done in FindTrainCollideEnum() to minimum

This commit is contained in:
smatz 2009-06-23 23:31:43 +00:00
parent 0045096403
commit 986cc75a12
1 changed files with 6 additions and 2 deletions
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8
src/train_cmd.cpp
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@ -3561,8 +3561,12 @@ static Vehicle *FindTrainCollideEnum(Vehicle *v, void *data)
int x_diff = v->x_pos - tcc->v->x_pos;
int y_diff = v->y_pos - tcc->v->y_pos;
/* needed to disable possible crash of competitor train in station by building diagonal track at its end */
if (x_diff * x_diff + y_diff * y_diff > 25) return NULL;
/* Needed to disable possible crash of competitor train in station by building diagonal track at its end.
* The second check is false when (abs(first), abs(second)) is: a) 5, 0 b) 4, <=3 c) 3, <=4, d) 2-, <=5
* Sum of these two is at most 2 + 5 == 4 + 3 == 7. So we can just test if sum of abs() is > 7 to prevent
* multiplying. Simply, when sum of abs() is >= 8, the sum of squares can't be <= 25.
* Even gcc3.4 seems to do abs() branchless (using arithmetics or conditional moves). */
if (abs(x_diff) + abs(y_diff) > 7 || x_diff * x_diff + y_diff * y_diff > 25) return NULL;
/* crash both trains */
tcc->num += TrainCrashed(Train::From(tcc->v));