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LOGB
Linux Programmer's Manual (3)
20140228
NAME
logb, logbf, logbl  get exponent of a floatingpoint value
SYNOPSIS
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);
Link with lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
logb():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 500 
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
logbf(),
logbl():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or
cc std=c99
DESCRIPTION
These functions extract the exponent from the
internal floatingpoint representation of
x
and return it as a floatingpoint value.
The integer constant
FLT_RADIX,
defined in
<float.h>,
indicates the radix used for the system's floatingpoint 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 dividebyzero floatingpoint exception
(FE_DIVBYZERO)
is raised.
These functions do not set
errno.
ATTRIBUTES
Multithreading (see pthreads(7))
The
logb(),
logbf(),
and
logbl()
functions are threadsafe.
CONFORMING TO
C99, POSIX.12001.
SEE ALSO
ilogb(3),
log(3)
COLOPHON
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Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 ATTRIBUTES

 Multithreading (see pthreads(7))

 CONFORMING TO

 SEE ALSO

 COLOPHON

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Time: 21:43:01 GMT, July 12, 2014