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NAME
       log, logf, logl - natural logarithm function


SYNOPSIS
       #include <math.h>

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


DESCRIPTION
       These functions shall compute the natural logarithm of their argument x, log_e(x).

       An   application   wishing   to   check   for  error  situations  should  set  errno  to  zero  and  call
       feclearexcept(FE_ALL_EXCEPT) before calling  these  functions.   On  return,  if  errno  is  non-zero  or
       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.


RETURN VALUE
       Upon successful completion, these functions shall return the natural logarithm of x.

       If  x  is  ±0, a pole error shall occur and log(), logf(), and logl() shall return -HUGE_VAL, -HUGE_VALF,
       and -HUGE_VALL, respectively.

       For finite values of x that are less than 0,    or if x  is  -Inf,   a  domain  error  shall  occur,  and
        either a NaN (if supported), or   an implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is 1, +0 shall be returned.

       If x is +Inf, x shall be returned.


ERRORS
       These functions shall fail if:

       Domain Error
              The finite value of x is negative,    or x is -Inf.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM].
       If  the  integer  expression  (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-
       point exception shall be raised.

       Pole Error
              The value of x is zero.

       If the integer expression (math_errhandling & MATH_ERRNO)  is  non-zero,  then  errno  shall  be  set  to
       [ERANGE].  If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-
       zero floating-point exception shall be raised.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       On error, the expressions (math_errhandling & MATH_ERRNO) and  (math_errhandling  &  MATH_ERREXCEPT)  are
       independent of each other, but at least one of them must be non-zero.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       exp()  ,  feclearexcept() , fetestexcept() , isnan() , log10() , log1p() , the Base Definitions volume of
       IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>


COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                                LOG(P)