log1p(3)                   Library Functions Manual                   log1p(3)

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
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

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)

Linux man-pages 6.7               2023-10-31                          log1p(3)