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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON |
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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():
_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
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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├─────────────────────────┼───────────────┼─────────┤
│logb(), logbf(), logbl() │ Thread safety │ MT-Safe │
└─────────────────────────┴───────────────┴─────────┘
C99, POSIX.1-2001, POSIX.1-2008.
ilogb(3), log(3)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 LOGB(3)
Pages that refer to this page: ilogb(3), remquo(3)
Copyright and license for this manual page
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