1.29 ilogb, ilogbf—get exponent of floating-point number

Synopsis

#include <math.h>
int ilogb(double val);
int ilogbf(float val);

Description

All nonzero, normal numbers can be described as m * 2**p. ilogb and ilogbf examine the argument val, and return p. The functions frexp and frexpf are similar to ilogb and ilogbf, but also return m.

Returns

ilogb and ilogbf return the power of two used to form the floating-point argument. If val is 0, they return FP_ILOGB0. If val is infinite, they return INT_MAX. If val is NaN, they return FP_ILOGBNAN. (FP_ILOGB0 and FP_ILOGBNAN are defined in math.h, but in turn are defined as INT_MIN or INT_MAX from limits.h. The value of FP_ILOGB0 may be either INT_MIN or -INT_MAX. The value of FP_ILOGBNAN may be either INT_MAX or INT_MIN.)

Portability
C99, POSIX