/* @(#)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. * ==================================================== * */ #ifndef lint static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_atanh.c,v 1.7 2005/02/04 18:26:05 das Exp $"; #endif /* atanh(x) * Method : * 1.Reduced x to positive by atanh(-x) = -atanh(x) * 2.For x>=0.5 * 1 2x x * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------) * 2 1 - x 1 - x * * For x<0.5 * atanh(x) = 0.5*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 "math.h" #include "math_private.h" static const double one = 1.0, huge = 1e300; static const double zero = 0.0; double atanh(double x) { double t; int32_t hx,ix; u_int32_t lx; EXTRACT_WORDS(hx,lx,x); 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 */ SET_HIGH_WORD(x,ix); if(ix<0x3fe00000) { /* x < 0.5 */ t = x+x; t = 0.5*log1p(t+t*x/(one-x)); } else t = 0.5*log1p((x+x)/(one-x)); if(hx>=0) return t; else return -t; }