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LOG1P
Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
Index
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NAME
log1p, log1pf, log1pl - logarithm of 1 plus argument
SYNOPSIS
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
log1p():
-
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
log1pf(),
log1pl():
-
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or
cc -std=c99
DESCRIPTION
log1p(x)
returns a value equivalent to
log (1 + x)
It is computed in a way
that is accurate even if the value of x is near zero.
RETURN VALUE
On success, these functions return the natural logarithm of
(1 + x).
If
x
is a NaN,
a NaN is returned.
If
x
is positive infinity, positive infinity is returned.
If
x
is -1, a pole error occurs,
and the functions return
-HUGE_VAL,
-HUGE_VALF,
or
-HUGE_VALL,
respectively.
If
x
is less than -1 (including negative infinity),
a domain error occurs,
and a NaN (not a number) 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:
- Domain error: x is less than -1
-
An invalid floating-point exception
(FE_INVALID)
is raised.
- Pole error: x is -1
-
A divide-by-zero floating-point exception
(FE_DIVBYZERO)
is raised.
These functions do not set
errno.
CONFORMING TO
C99, POSIX.1-2001.
SEE ALSO
exp(3),
expm1(3),
log(3)
COLOPHON
This page is part of release 3.27 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- SEE ALSO
-
- COLOPHON
-
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