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/* @(#)e_atanh.c 1.3 95/01/18 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*
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*/
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/* __ieee754_atanh(x)
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* Method :
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* 1.Reduced x to positive by atanh(-x) = -atanh(x)
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* 2.For x>=0.5
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* 1 2x x
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* atanh(x) = --- * ieee_log(1 + -------) = 0.5 * ieee_log1p(2 * --------)
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* 2 1 - x 1 - x
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*
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* For x<0.5
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* atanh(x) = 0.5*ieee_log1p(2x+2x*x/(1-x))
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*
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* Special cases:
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* atanh(x) is NaN if |x| > 1 with signal;
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* atanh(NaN) is that NaN with no signal;
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* atanh(+-1) is +-INF with signal.
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*
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*/
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#include "fdlibm.h"
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#ifdef __STDC__
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static const double one = 1.0, huge = 1e300;
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#else
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static double one = 1.0, huge = 1e300;
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#endif
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static double zero = 0.0;
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#ifdef __STDC__
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double __ieee754_atanh(double x)
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#else
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double __ieee754_atanh(x)
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double x;
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#endif
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{
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double t;
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int hx,ix;
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unsigned lx;
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hx = __HI(x); /* high word */
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lx = __LO(x); /* low word */
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ix = hx&0x7fffffff;
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if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */
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return (x-x)/(x-x);
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if(ix==0x3ff00000)
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return x/zero;
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if(ix<0x3e300000&&(huge+x)>zero) return x; /* x<2**-28 */
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__HI(x) = ix; /* x <- |x| */
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if(ix<0x3fe00000) { /* x < 0.5 */
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t = x+x;
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t = 0.5*ieee_log1p(t+t*x/(one-x));
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} else
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t = 0.5*ieee_log1p((x+x)/(one-x));
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if(hx>=0) return t; else return -t;
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}
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