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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 .