frexp() - convert floating-point number to fractional and integral components
#include <math.h>
double frexp (double value, int *exp)
The frexp(3) function breaks a floating-point number into a normalized fraction and an integral power of 2. It stores the integer in the int object pointed to by exp.
Frexp(3) is the inverse of ldexp(3).
The frexp(3) function returns the value x, such that x is a double with magnitude in the interval [1/2, 1) or zero, and value equals x times 2 raised to the power *exp. If value is zero, both parts of the result are zero.
ldexp(3)
modf(3)