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[/] [openrisc/] [trunk/] [gnu-old/] [newlib-1.17.0/] [newlib/] [libm/] [math/] [e_atanh.c] - Blame information for rev 855

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1 148 jeremybenn
 
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/* @(#)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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 */
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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 "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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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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#ifdef __STDC__
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static const double zero = 0.0;
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#else
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static double zero = 0.0;
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#endif
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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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        __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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#endif /* defined(_DOUBLE_IS_32BITS) */

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