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 ||
_ISOC99_SOURCE; or cc -std=c99
log1pf(), log1pl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; 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 3.24 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/.
2008-08-05