Avoiding denormal values in C++

Question

After searching a long time for a performance bug, I read about denormal floating point values.

Apparently denormalized floating-point values can be a major performa

Answer 1

You can test whether a float is denormal using

#include 

if ( std::fpclassify( flt ) == FP_SUBNORMAL )

(Caveat: I'm not sure that this will execute at full speed in practice.)

In C++03, and this code has worked for me in practice,

#include 
#include 

if ( flt != 0 && std::fabsf( flt ) < std::numeric_limits::min() ) {
    // it's denormalized
}

To decide where to apply this, you may use a sample-based analyzer like Shark, VTune, or Zoom, to highlight the instructions slowed by denormal values. Micro-optimization, even more than other optimizations, is totally hopeless without analysis both before and after.