LOG1P(3)		   Linux Programmer's Manual		      LOG1P(3)



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():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
	       || _XOPEN_SOURCE >= 500
	       || /* Since glibc 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
       log1pf(), log1pl():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
	       || /* Since glibc 2.19: */ _DEFAULT_SOURCE
	       || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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 |
       +----------------------------+---------------+---------+
CONFORMING TO
       C99, POSIX.1-2001, POSIX.1-2008.

SEE ALSO
       exp(3), expm1(3), log(3)

COLOPHON
       This  page  is  part of release 4.10 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/.



				  2016-03-15			      LOG1P(3)