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/* Copyright (C) 1991 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#include <ansidecl.h>
#include <errno.h>
#include <math.h>
/* Return the inverse cosine of X. */
double
DEFUN(acos, (x), double x)
{
double t;
if (__isnan(x))
{
errno = EDOM;
return x;
}
if (x == -1.0)
/* If X is -1, the general formula blows up (zero divided by zero loses),
but we know that acos(-1) = pi. */
t = atan2(1.0, 0.0);
else
t = atan2(sqrt((1.0 - x) / (1.0 + x)), 1.0);
return t + t;
}
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