Re: BUG #6675: Box overlap with infinity edge

jeremie(dot)thomassey(at)gmail(dot)com writes:
> I can't understand this result :

> SELECT box '((1,1),(infinity, 1))' && box '((2, 1),(infinity, 1))';
> ?column?
> ---------
> f

> Isn't it supposed to return true? The documentation doesn't really say
> anything about infinite edge.

The test for this involves

FPge(box1->high.x, box2->high.x)

where FPge is defined as

#define FPge(A,B) ((B) - (A) <= EPSILON)

When both high.x values are infinity, you have infinity minus infinity,
which yields NaN in IEEE arithmetic, so the comparison to epsilon comes
out false.

In general I don't think we promise that geometric operations involving
infinite endpoints will behave sanely. There are probably a boatload
of corner cases besides this one that'd need to be fixed before we
could consider that a supported case.

regards, tom lane