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LOG10(3P)                  POSIX Programmer's Manual                 LOG10(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       log10, log10f, log10l - base 10 logarithm function
SYNOPSIS
       #include <math.h>
       double log10(double x);
       float log10f(float x);
       long double log10l(long double x);

DESCRIPTION
       These functions shall compute the base 10 logarithm of  their  argument
       x, log_10(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 base 10
       logarithm of x.
       If x is +-0, a pole  error  shall  occur  and  log10(),  log10f(),  and
       log10l()  shall  return  -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respec-
       tively.
       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, +Inf 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
       feclearexcept(), fetestexcept(), isnan(), log(), pow(), the Base  Defi-
       nitions  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                            LOG10(3P)