1 /* origin: FreeBSD /usr/src/lib/msun/src/e_atanh.c */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 * Developed at SunSoft, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
10 * ====================================================
15 * 1.Reduced x to positive by atanh(-x) = -atanh(x)
18 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
22 * atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
25 * atanh(x) is NaN if |x| > 1 with signal;
26 * atanh(NaN) is that NaN with no signal;
27 * atanh(+-1) is +-INF with signal.
33 static const double one = 1.0, huge = 1e300;
34 static const double zero = 0.0;
36 double atanh(double x)
42 EXTRACT_WORDS(hx, lx, x);
44 if ((ix | ((lx|-lx)>>31)) > 0x3ff00000) /* |x| > 1 */
48 if (ix < 0x3e300000 && (huge+x) > zero) /* x < 2**-28 */
51 if (ix < 0x3fe00000) { /* x < 0.5 */
53 t = 0.5*log1p(t + t*x/(one-x));
55 t = 0.5*log1p((x+x)/(one-x));