Best way to detect NaN's in OpenGL shaders

Question

I ran into what seemed a mysterious bug this morning that I feel very lucky to have stumbled upon a solution for quite quickly.

I was dividing by a counter to produce a

Answer 1

Lack of isnan is problem for WebGL and Opengl ES 2.0. Polyfill which works for all GPUs I had an opportunity to try:

bool isnan( float val )
{
  return ( val < 0.0 || 0.0 < val || val == 0.0 ) ? false : true;
  // important: some nVidias failed to cope with version below.
  // Probably wrong optimization.
  /*return ( val <= 0.0 || 0.0 <= val ) ? false : true;*/
}