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