NAME

       acos, acosf, acosl - arc cosine functions

SYNOPSIS

       #include <math.h>

       double acos(double x);
       float acosf(float x);
       long double acosl(long double x);

DESCRIPTION

       These  functions  shall compute the principal value of the arc cosine of their argument x.
       The value of x should be in the range [-1,1].

       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 arc cosine of x, in the range
       [0,pi] radians.

       For finite values of x not in the range [-1,1], 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,  a  domain  error  shall  occur,  and  either a NaN (if supported), or an
       implementation-defined value shall be returned.

ERRORS

       These functions shall fail if:

       Domain Error
              The x argument is finite and is not in the range [-1,1],    or 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.

       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

       cos()  ,  feclearexcept()  ,  fetestexcept()  ,  isnan()  , 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 .