ILOGB(3)

NAME
ilogb, ilogbf, ilogbl - get integer exponent of a floating point value

SYNOPSIS
#include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);

Link with -lm.

DESCRIPTION
These functions return the exponent part of their argument as a signed integer. When no error occurs, these functions are equivalent to the corresponding logb(3) functions, cast to (int). An error will occur for zero and infinity and NaN, and possibly for overflow.

ERRORS
In order to check for errors, set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is nonzero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, an error has occurred.

If an error occurs and (math_errhandling & MATH_ERRNO) is nonzero, then errno is set to EDOM. If an error occurs and (math_errhandling & MATH_ERREXCEPT) is nonzero, then the invalid floating-point exception is raised.

A domain error occurs when x is zero or infinite (or too large, or too small) or NaN. If x is zero, the constant FP_ILOGB0 is returned. If x is NaN, the constant FP_ILOGBNAN is returned. If x is infinite (or too large), INT_MAX is returned. If x is too small, INT_MIN is returned.

CONFORMING TO
C99

SEE ALSO
log(3), logb(3)

COLOPHON
This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.