RE: Strange float bug?

Sounds like a and/or b is set to an SNaN prior to this line, so you'll
want to figure out how that's happening.  I'd be willing to bet that
you're dereferencing a bad float pointer or indexing outside of a float
array, which would explain why the exception has been sporadic.  (FPU
ops never generate SNaNs.)

Denormalized values are a different issue and shouldn't result in a NaN
under add and subtract operations.  Also note that _controlfp doesn't
affect the denormal exception mask on x86.

Donavon Keithley


> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of
> Brett Bibby
> Sent: Sunday, March 07, 2004 7:39 AM
> To: [email protected]
> Subject: [GD-Windows] Strange float bug?
> 
> We have been tracking down the wierdest bug for several days. Our code
was
> crashing randomly and then we finally found a repeatable case where an
> assert on an identity matrix when we check the orthonormalness of it
and
> we chanced upon a line of code that returned -nan that was simply x =
> (1.0f - (a + b)).  Anyway, I suddenly remembered a GDC talk about
Windows
> denormals, did a quick google and pasted a _controlfp( _CW_DEFAULT,
> 0xfffff ) into our code and presto it now works.
> 
> We make games for PS2 and GCN and are Windows amateurs, but I hate the
> idea of not understanding what went wrong and how to properly handle
this.
> Has anybody ever encountered something like this before?
> 
> Brett
> 
> 
> 
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