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man:log

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

NAME

     log, logf, logl - natural logarithmic function

SYNOPSIS

     #include <math.h>
     double log(double x);
     float logf(float x);
     long double logl(long double x);
     Link with -lm.
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     logf(), logl():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

     These functions return the natural logarithm of x.

RETURN VALUE

     On success, these functions return the natural logarithm of x.
     If x is a NaN, a NaN is returned.
     If x is 1, the result is +0.
     If x is positive infinity, positive infinity is returned.
     If  x  is  zero,  then  a  pole  error occurs, and the functions return
     -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
     If x is negative (including negative infinity),  then  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 negative
            errno is set  to  EDOM.   An  invalid  floating-point  exception
            (FE_INVALID) is raised.
     Pole error: x is zero
            errno  is set to ERANGE.  A divide-by-zero floating-point excep-
            tion (FE_DIVBYZERO) is raised.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).
     +----------------------+---------------+---------+
     |Interface             | Attribute     | Value   |
     +----------------------+---------------+---------+
     |log(), logf(), logl() | Thread safety | MT-Safe |
     +----------------------+---------------+---------+

CONFORMING TO

     C99, POSIX.1-2001, POSIX.1-2008.
     The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS

     In glibc 2.5 and earlier, taking the log() of a NaN  produces  a  bogus
     invalid floating-point (FE_INVALID) exception.

SEE ALSO

     cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)

COLOPHON

     This  page  is  part of release 4.16 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                            LOG(3)
/data/webs/external/dokuwiki/data/pages/man/log.txt · Last modified: 2019/05/17 09:32 by 127.0.0.1

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