log1p(3) — Linux manual page


LOG1P(3)                Linux Programmer's Manual               LOG1P(3)

NAME         top

       log1p, log1pf, log1pl -  logarithm of 1 plus argument

SYNOPSIS         top

       #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

           _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         top

       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         top

       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         top

       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         top

       For an explanation of the terms used in this section, see

       │Interface                             Attribute     Value   │
       │log1p(), log1pf(), log1pl()           │ Thread safety │ MT-Safe │

CONFORMING TO         top

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

BUGS         top

       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         top

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

COLOPHON         top

       This page is part of release 5.13 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

                               2021-03-22                       LOG1P(3)

Pages that refer to this page: expm1(3)log(3)