Re: problem with output of the program on different OS

Bart <bc@[EMAIL PROTECTED]
> writes:

> On May 13, 1:58 pm, Ben Bacarisse <ben.use...@[EMAIL PROTECTED]
> wrote:
>> Bart <b...@[EMAIL PROTECTED]
> writes:
>> > There's lots of other uninitialised data which may or may not be
>> > affecting anything else. However the 7.08/7.39 discrepancy *was*
>> > traced to these zero/near zero values.
>>
>> Then the problem (or the algorithm) may be unstable, but I am not
>> persuaded that the compiler was wrong to produce 0 for the arithmetic
>> test case you posted a while back.
>
> There was a /possibility/ of a compiler bug, but until I found one
> reason for the discrepancy, we didn't know that for sure. Now it seems
> Pelles was correct and the others wrong!

I think that is a stretch.  I know you mean that the others did not
reveal something that you feel was im****tant, but it is going some to
get from that to the other compilers are wrong!

> (Because by chance Pelles
> avoid the near-zero values that caused the indeterminancy later on.)
>
> A proper fix is now up to the OP; I've already suggested care testing
> values against /exactly/ 0.0 or 1.0.

I agree that only the OP can really sort this out but in general I
think your advice is too strict.  Testing for exactly *equal* to zero
is obviously problematic but deciding if a ray does or does intersect
a triangle using code like if (v < 0 || v > 1) should be fine.  If
including of excluding a few edge rays causes a significant change to
the results it suggests that something else is wrong.

-- 
Ben.