logb():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or
cc -std=c99 logbf(),
logbl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or
cc -std=c99
DESCRIPTION
These functions extract the exponent from the
internal floating-point representation of
x
and return it as a floating-point value.
The integer constant
FLT_RADIX,
defined in
<float.h>,
indicates the radix used for the system's floating-point representation.
If
FLT_RADIX
is 2,
logb(x)
is equal to
floor(log2(x)),
except that it is probably faster.
If
x
is subnormal,
logb()
returns the exponent
x
would have if it were normalized.
RETURN VALUE
On success, these functions return the exponent of
x.
If
x
is a NaN,
a NaN is returned.
If
x
is zero, then a pole error occurs, and the functions return
-HUGE_VAL,
-HUGE_VALF,
or
-HUGE_VALL,
respectively.
If
x
is negative infinity or positive infinity, then
positive infinity is returned.
ERRORS
See
math_error(7)
for information on how to determine whether an error has occurred
when calling these functions.
The following errors can occur:
Pole error: x is 0
A divide-by-zero floating-point exception
(FE_DIVBYZERO)
is raised.
This page is part of release 3.14 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/.
