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/* @(#)s_asinh.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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#ifndef lint
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static char rcsid[] = "$\Id: s_asinh.c,v 1.2 1995/05/30 05:49:18 rgrimes Exp $";
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#endif
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/* asinh(x)
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 * Method :
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 *      Based on
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 *              asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
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 *      we have
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 *      asinh(x) := x  if  1+x*x=1,
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 *               := sign(x)*(log(x)+ln2)) for large |x|, else
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 *               := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
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 *               := sign(x)*log1p(|x| + x^2/(1 + sqrt(1+x^2)))
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 */
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#include "math.h"
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#include "math_private.h"
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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one =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
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ln2 =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
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huge=  1.00000000000000000000e+300;
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#ifdef __STDC__
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        double asinh(double x)
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#else
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        double asinh(x)
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        double x;
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#endif
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{
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        double t,w;
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        int32_t hx,ix;
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        GET_HIGH_WORD(hx,x);
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        ix = hx&0x7fffffff;
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        if(ix>=0x7ff00000) return x+x;  /* x is inf or NaN */
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        if(ix< 0x3e300000) {    /* |x|<2**-28 */
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            if(huge+x>one) return x;    /* return x inexact except 0 */
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        }
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        if(ix>0x41b00000) {     /* |x| > 2**28 */
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            w = __ieee754_log(fabs(x))+ln2;
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        } else if (ix>0x40000000) {     /* 2**28 > |x| > 2.0 */
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            t = fabs(x);
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            w = __ieee754_log(2.0*t+one/(sqrt(x*x+one)+t));
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        } else {                /* 2.0 > |x| > 2**-28 */
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            t = x*x;
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            w =log1p(fabs(x)+t/(one+sqrt(one+t)));
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        }
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        if(hx>0) return w; else return -w;
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}