log(3M)

NAME

     log - natural logarithm function

SYNOPSIS

     cc [ flag ... ] file ... -lm [ library ... ]
     #include <math.h>

     double log(double x);

DESCRIPTION

     The log() function computes  the  natural  logarithm  of  x,
     loge(x). The value of x must be positive.

RETURN VALUES

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

     If x is NaN, NaN is returned.

     If x is less than 0, -HUGE_VAL or NaN is returned and  errno
     is set to EDOM.

     If x is 0, -HUGE_VAL is returned and errno  may  be  set  to
     ERANGE.

     In IEEE754 mode (the -Xlibmieee cc compilation option), if x
     is  Inf  or  a quiet NaN, x is returned; if x is a signaling
     NaN, a quiet NaN  is  returned  and  the  invalid  operation
     exception is raised; if x is 1, 0 is returned; for all other
     positive x, a normalized number is returned and the  inexact
     exception is raised.

     For exceptional cases, matherr(3M) tabulates the  values  to
     be returned as dictated by Standards other than XPG4.

ERRORS

     The log() function will fail if:

     EDOM  The value of x is negative.

     The log() function may fail if:

     ERANGE
           The value of x is 0.

     No other errors will occur.

USAGE

     An application wishing to check for error situations  should
     set errno to 0 before calling log(). If errno is non-zero on
     return, or the return value is NaN, an error has occurred.

ATTRIBUTES

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

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|

SEE ALSO

     exp(3M),  isnan(3M),  log10(3M),   log1p(3M),   matherr(3M),
     attributes(5), standards(5)