Returns an unbiased exponent.
#include <math.h>
int ilogbf (x)
float x;
int ilogbl (x)
long double x;
int ilogb (x)
double x;The ilogbf, ilogbl, and ilogb subroutines return the exponent part of the x parameter. The return value is the integral part of logr | x | as a signed integral value, for nonzero x, where r is the radix of the machine's floating-point arithmetic (r=2).
An application wishing to check for error situations should set thre errno global variable to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these subroutines. Upon return, if errno is nonzero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, an error has occurred.
| Item | Description |
|---|---|
| x | Specifies the value to be computed. |
Upon successful completion, the ilogbf, ilogbl, and ilogb subroutines return the exponent part of x as a signed integer value. They are equivalent to calling the corresponding logb function and casting the returned value to type int.
If x is 0, a domain error occurs, and the value FP_ILOGB0 is returned.
If x is ±Inf, a domain error occurs, and the value {INT_MAX} is returned.
If x is a NaN, a domain error occurs, and the value FP_ILOGBNAN is returned.
If the correct value is greater than {INT_MAX}, {INT_MAX} is returned and a domain error occurs.
If the correct value is less than {INT_MIN}, {INT_MIN} is returned and a domain error occurs.