NAME

       log1p, log1pf, log1pl -  logarithm of 1 plus argument

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       double log1p(double x);
       float log1pf(float x);
       long double log1pl(long double x);

   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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       log1pf(), log1pl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

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

BUGS

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

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

SEE ALSO

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