#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)):

           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
           _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

       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.

       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.

       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

       C99, POSIX.1-2001, POSIX.1-2008.

       exp(3), expm1(3), log(3)

       This page is part of release 4.04 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

                                  2015-04-19                          LOG1P(3)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2019 Hurricane Electric. All Rights Reserved.