2.7.3.2 frexp

Declaration:

double frexp(double x, int *exponent);The floating-point number x is broken up into a mantissa and exponent.
The returned value is the mantissa and the integer pointed to by exponent is the exponent. The resultant value is x=mantissa * 2^exponent.

Range:

The mantissa is in the range of .5 (inclusive) to 1 (exclusive).