log1p (3)
Leading comments
Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
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NAME
log1p, log1pf, log1pl - logarithm of 1 plus argumentSYNOPSIS
#include <math.h> double log1p(double x);Link with -lm.
float log1pf(float x);
long double log1pl(long double x);
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
These functions return a value equivalent to
log (1 + x)
The result 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| log1p(), log1pf(), log1pl() | Thread safety | MT-Safe |