log1p

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
                                  2008-08-05                          LOG1P(3)