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

[Will Schroeder]

Hi Folks-

I was profiling VTK and discovered a couple of issues with vtkMath. The 
fabs() function (used in LUSolve, etc) is taking an surprising amount of 
time, and I find some leftover static variables. Here's what I'm 
thinking---I'd like your comments.

fabs()
We can define a macro #define  VTK_FABS(x)  (x) < 0.0 )?(-(x)):(x))
Another alternative is to do what vnl does:
inline float       VTK_FABS(float  x) { return ::fabsf(x); }
inline double      VTK_FABS(double x) { return ::fabs(x); }

The macro seems to be a bit faster but I'm running debug not release.

Static variables will be replaced with code like this that is partially 
optimized for small matrices:
 >   int *index, scratch[10];
 >   index = ( size < 10 ? scratch : new int[size] );
 >   if (size >= 10 ) delete [] index;

Comments?

Will