ILOGB(3) Linux Programmer's Manual ILOGB(3)
ilogb, ilogbf, ilogbl - get integer exponent of a floating point value
int ilogb(double x);
int ilogbf(float x);
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 feclearex-
cept(FE_ALL_EXCEPT) before calling these functions. On return, if
errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVER-
FLOW | 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 EDOM. If an error occurs and (math_errhandling &
MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception
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.
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