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-/*
- * Copyright (c) 1985, 1993
- * The Regents of the University of California. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- * must display the following acknowledgement:
- * This product includes software developed by the University of
- * California, Berkeley and its contributors.
- * 4. Neither the name of the University nor the names of its contributors
- * may be used to endorse or promote products derived from this software
- * without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#ifndef lint
-static char sccsid[] = "@(#)atanh.c 8.1 (Berkeley) 6/4/93";
-#endif /* not lint */
-
-/* ATANH(X)
- * RETURN THE HYPERBOLIC ARC TANGENT OF X
- * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
- * CODED IN C BY K.C. NG, 1/8/85;
- * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
- *
- * Required kernel function:
- * log1p(x) ...return log(1+x)
- *
- * Method :
- * Return
- * 1 2x x
- * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
- * 2 1 - x 1 - x
- *
- * Special cases:
- * atanh(x) is NaN if |x| > 1 with signal;
- * atanh(NaN) is that NaN with no signal;
- * atanh(+-1) is +-INF with signal.
- *
- * Accuracy:
- * atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
- * In a test run with 512,000 random arguments on a VAX, the maximum
- * observed error was 1.87 ulps (units in the last place) at
- * x= -3.8962076028810414000e-03.
- */
-#include "mathimpl.h"
-
-#if defined(vax)||defined(tahoe)
-#include <errno.h>
-#endif /* defined(vax)||defined(tahoe) */
-
-double atanh(x)
-double x;
-{
- double z;
- z = copysign(0.5,x);
- x = copysign(x,1.0);
-#if defined(vax)||defined(tahoe)
- if (x == 1.0) {
- return(copysign(1.0,z)*infnan(ERANGE)); /* sign(x)*INF */
- }
-#endif /* defined(vax)||defined(tahoe) */
- x = x/(1.0-x);
- return( z*log1p(x+x) );
-}