log1pf (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> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting deriv...
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 tolog (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 floatingpoint exception (FE_INVALID) is raised.
 Pole error: x is 1
 A dividebyzero floatingpoint 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  MTSafe 