[Issue 3751] Optimalization error in some floating point code

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3751



--- Comment #8 from Steven Schveighoffer <schveiguy at yahoo.com> 2010-01-29 06:06:41 PST ---
(In reply to comment #7)
> Yes I know, but I was relaying of IEEE 754 semantic, in which my code should
> work (there will be point in execuion when left == half or right == half
> exactly!). I was just trying to write this routine to be slightly faster just
> by not using EPSILONS and substractions.

Are you sure?  I'm not really a floating point expert, so I don't know what the
rules of IEEE are, but I have written floating point convergence algorithms for
things like programming competitions, and I had to learn that things will get
stuck if you don't use an epsilon.

You can picture what's happening if you make left and right integers.  What
ends up happening when left - right == 1?  half becomes left + .5, so it does
not compare equal to left or right, but if your calculation then assigns left
equal to half, the .5 is dropped and left is stuck in the same loop.

I would say that this is not a bug, but again, not a floating point expert.

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