#include <math.h>


float frexpf( float num, int* exp );
The function frexpf() is used to decompose num into two parts: 
a mantissa between 0.5 and 1 (returned by the function) and an 
exponent returned as exp. Scientific notation works like this:
 
   num = mantissa * (2 ^ exp)           
 
Related topics: 
ldexp
modf