ilogb

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

#include <math.h> I int ilogb(double x );
I int ilogbf(float x );
I int ilogbl(long double x ); Link with -lm.

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.

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 non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

If an error occurs and (math_errhandling & MATH_ERRNO) is non-zero, then errno is set to R EDOM . If an error occurs and (math_errhandling & MATH_ERREXCEPT) is non-zero, 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.

C99

log(3), logb(3)