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
              errno is  set  to  EDOM  (but  see  BUGS).   An  invalid  floating-point  exception
              (FE_INVALID) is raised.

       Pole error: x is -1
              errno  is  set to ERANGE (but see BUGS).  A divide-by-zero floating-point exception
              (FE_DIVBYZERO) is raised.

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.

BUGS

       Before version 2.22, the glibc implementation did not set errno  to  EDOM  when  a  domain
       error occurred.

       Before  version  2.22,  the  glibc implementation did not set errno to ERANGE when a range
       error occurred.

SEE ALSO

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

COLOPHON

       This page is part of release 5.05 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/.

                                            2017-09-15                                   LOG1P(3)