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

NAME
       log, logf, logl - natural logarithmic function

SYNOPSIS
       #include 

       double log(double x);
       float logf(float x);
       long double logl(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see featuretestmacros(7)):

       logf(), logl():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 600 ||
           ISOC99SOURCE || POSIXCSOURCE >= 200112L;
           or cc -std=c99

DESCRIPTION
       The log() function returns 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
       -HUGEVAL, -HUGEVALF, or -HUGEVALL, respectively.

       If  x  is  negative  (including negative infinity), then a domain error
       occurs, and a NaN (not a number) is returned.

ERRORS
       See matherror(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
              (FEINVALID) is raised.

       Pole error: x is zero
              errno is set to ERANGE.  A divide-by-zero floating-point  excep‐
              tion (FEDIVBYZERO) is raised.

CONFORMING TO
       C99, POSIX.1-2001.  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 (FEINVALID) exception.

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

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



                                  2010-09-20                            LOG(3)