Mathematical Library Functions                            log(3M)



NAME
     log, logf, logl - natural logarithm function

SYNOPSIS
     c99 [ flag... ] file... -lm [ library... ]
     #include 

     double log(double x);


     float logf(float x);


     long double logl(long double x);


DESCRIPTION
     These functions compute the natural logarithm of their argu-
     ment x, log(e)(x).

RETURN VALUES
     Upon successful completion, log() returns the natural  loga-
     rithm of x.


     If x is ]0, a pole  error  occurs  and  log(),  logf(),  and
     logl() return -HUGEVAL, -HUGEVALF, and -HUGEVAL, respec-
     tively.


     For finite values of x that are less than  0,  or  if  x  is
     -Inf, a domain error occurs and a NaN is returned.


     If x is NaN, a NaN is returned.


     If x is 1, ]0 is returned.


     If x is ]Inf, x is returned.


     For exceptional cases, matherr(3M) tabulates the  values  to
     be returned by log() as specified by SVID3 and XPG3.

ERORS
     These functions will fail if:

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




SunOS 5.11          Last change: 12 Jul 2006                    1






Mathematical Library Functions                            log(3M)



                     If the integer expression  (matherrhandling
                     &  MATHEREXCEPT)  is non-zero, the invalid
                     floating-point exception is raised.

                     The log() function sets errno to EDOM if the
                     value of x is negative.


     Pole Error      The value of x is 0.

                     If the integer expression  (matherrhandling
                     &  MATHEREXCEPT)  is non-zero, the divide-
                     by-zero floating-point exception is raised.


USAGE
     An application wanting to check for exceptions  should  call
     feclearexcept(FEALEXCEPT) before calling these functions.
     On  return,  if  fetestexcept(FEINVALID    FEDIVBYZERO  
     FEOVERFLOW    FEUNDERFLOW)  is non-zero, an exception has
     been raised. An application should either examine the return
     value  or check the floating point exception flags to detect
     exceptions.


     An application can also set errno to 0 before calling log().
     On  return, if errno is non-zero, an error has occurred. The
     logf() and logl() functions do not set errno.

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Standard                    
    
     MT-Level                     MT-Safe                     
    


SEE ALSO
     exp(3M),  feclearexcept(3M),  fetestexcept(3M),   isnan(3M),
     log10(3M),  log1p(3M),  math.h(3HEAD),  matherr(3M),  attri-
     butes(5), standards(5)







SunOS 5.11          Last change: 12 Jul 2006                    2