| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON | The Linux Programming Interface |
LOGB(3) Linux Programmer's Manual LOGB(3)
logb, logbf, logbl - get exponent of a floating-point value
#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
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.
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.
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.
C99, POSIX.1-2001.
ilogb(3), log(3)
This page is part of release 3.51 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/.
2010-09-20 LOGB(3)
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