5980be9b3c
This work is based in part on code from NetBSD libm, libc and kernel. The library is partly public domain and partly BSD-style licensed.
64 lines
1.6 KiB
C
64 lines
1.6 KiB
C
/* @(#)e_atanh.c 5.1 93/09/24 */
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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 SunPro, 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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#include <sys/cdefs.h>
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#if defined(LIBM_SCCS) && !defined(lint)
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__RCSID("$NetBSD: e_atanh.c,v 1.11 2002/05/26 22:01:49 wiz Exp $");
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#endif
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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) = --- * log(1 + -------) = 0.5 * 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*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 "math.h"
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#include "math_private.h"
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static const double one = 1.0, huge = 1e300;
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static const double zero = 0.0;
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double
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__ieee754_atanh(double x)
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{
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double t;
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int32_t hx,ix;
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uint32_t lx;
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EXTRACT_WORDS(hx,lx,x);
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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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SET_HIGH_WORD(x,ix);
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if(ix<0x3fe00000) { /* x < 0.5 */
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t = x+x;
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t = 0.5*log1p(t+t*x/(one-x));
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} else
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t = 0.5*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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