Manpage of LOGB

LOGB

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

logb, logbf, logbl - get exponent of a floating-point 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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || _XOPEN_SOURCE >= 500
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

logbf(), logbl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
 

DESCRIPTION

These functions extract the exponent from the internal floating-point representation of xand 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_RADIXis 2, logb(x)is equal to floor(log2(x)), except that it is probably faster.

If xis subnormal, logb() returns the exponent xwould have if it were normalized.  

RETURN VALUE

On success, these functions return the exponent of x.

If xis a NaN, a NaN is returned.

If xis zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

If xis 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.

These functions do not set errno.  

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
logb(), logbf(), logbl() Thread safetyMT-Safe
 

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.  

SEE ALSO

ilogb(3), log(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
SEE ALSO

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Time: 22:28:00 GMT, June 20, 2016