frexp - convert floating-point number to fractional and
double frexp(double x, int *exp));
The frexp() function is used to split the number x into a
normalized fraction and an exponent which is stored in exp.
The frexp() function returns the normalized fraction. If
the argument x is not zero, the normalized fraction is x
times a power of two, and is always in the range 1/2
(inclusive) to 1 (exclusive). If x is zero, then the nor-
malized fraction is zero and zero is stored in exp.
SVID 3, POSIX, BSD 4.3, ISO 9899