[vtk-developers] Possible changes to vtkMath...

[Chris Volpe]

The problem with that is that it brings us back to square one. It's not
much different from the fabs that the compiler provides already. It
won't be inlined on a non-optimized build. Since the issue that Will
raised is one of unnecessarily-poor performance on a debug build, it
doesn't seem useful to me to suggest alternatives that don't address
that issue. That's the same problem I see with Michael's suggestion to
use inline functions: on a build in which the function would be inlined,
the compiler-provided fabs would be an intrinsic, so there's no point. I
understand the desire to avoid the double side-effect evaluation, but I
personally think that, if improved performance on debug builds is, in
fact, desirable, then the risk inherent in the macro definition is
manageable. Just put a comment above the definition. You could even call
the macro VTK_UNSAFE_FABS and let people use plain ol' fabs when not in
a tight loop.

-Chris

> -----Original Message-----
> From: Andy Cedilnik [mailto:andy.cedilnik at kitware.com]
> Sent: Friday, July 11, 2003 9:04 AM
> To: Michael Halle
> Cc: Will Schroeder; vtk-developers at vtk.org
> Subject: RE: [vtk-developers] Possible changes to vtkMath...
> 
> Hi All,
> 
> How about template? That should be faster.
> 
> Something like
> 
> template <class DataType>
> DataType VTK_ABS(DataType d)
> {
>   return ((d < 0.0 ) ? (-d) : (d) );
> }
> 
> 			Andy
> 
> On Thu, 2003-07-10 at 19:47, Michael Halle wrote:
> > I don't like the idea of a fabs()-based macro because
> > of the double-evaluation side effects.  Conditionally
> > defining it only makes it worse. The ternary operator
> > may or may not be highly optimized on some platforms.
> >
> > Inlining is the defined mechanism for this purpose, even
> > if it may be slower on some platforms, I think it's the
> > best choice.
> > Michael Halle
> > mhalle at bwh.harvard.edu
> 
> 
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