NAME
ilogb, ilogbf,
ilogbl —
an unbiased exponent
LIBRARY
library “libm”
SYNOPSIS
#include
<math.h>
int
ilogb(double
x);
int
ilogbf(float
x);
int
ilogbl(long
double x);
DESCRIPTION
Theilogb(),
ilogbf(),
and
ilogbl()
functions return the exponent of the non-zero real floating-point number
x as a signed integer value. Formally the return value
is the integral part of
log_r | x |,
where r is the radix of the machine's
floating-point arithmetic defined by the FLT_RADIX
constant in <float.h>.
RETURN VALUES
As described above, upon successful completion, the functions return the exponent. Functionally this is the same as calling the corresponding logb(3) function and casting the return value to int.
The following special cases may occur:
- If x is zero, the value of
FP_ILOGB0is returned and a domain error occurs. - If x is infinite, a domain error occurs and the
value of
INT_MAXis returned. - If x is NaN, a domain error is raised and the value
of
FP_ILOGBNANis returned. - If the correct value is outside the range of the return type, a domain error occurs but an unspecified value is returned.
SEE ALSO
STANDARDS
The described functions conform to ISO/IEC 9899:1999 (“ISO C99”).