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 ||
           _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 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 4.04 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 http://www.kernel.org/doc/man-pages/.

                                            2015-04-19                                   LOG1P(3)