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 /* @(#)e_atanh.c 1.3 95/01/18 */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunSoft, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== * */ /* __ieee754_atanh(x) * Method : * 1.Reduced x to positive by atanh(-x) = -atanh(x) * 2.For x>=0.5 * 1 2x x * atanh(x) = --- * ieee_log(1 + -------) = 0.5 * ieee_log1p(2 * --------) * 2 1 - x 1 - x * * For x<0.5 * atanh(x) = 0.5*ieee_log1p(2x+2x*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. * */ #include "fdlibm.h" #ifdef __STDC__ static const double one = 1.0, huge = 1e300; #else static double one = 1.0, huge = 1e300; #endif static double zero = 0.0; #ifdef __STDC__ double __ieee754_atanh(double x) #else double __ieee754_atanh(x) double x; #endif { double t; int hx,ix; unsigned lx; hx = __HI(x); /* high word */ lx = __LO(x); /* low word */ ix = hx&0x7fffffff; if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */ return (x-x)/(x-x); if(ix==0x3ff00000) return x/zero; if(ix<0x3e300000&&(huge+x)>zero) return x; /* x<2**-28 */ __HI(x) = ix; /* x <- |x| */ if(ix<0x3fe00000) { /* x < 0.5 */ t = x+x; t = 0.5*ieee_log1p(t+t*x/(one-x)); } else t = 0.5*ieee_log1p((x+x)/(one-x)); if(hx>=0) return t; else return -t; }
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