1 /* from: FreeBSD: head/lib/msun/src/e_atanh.c 176451 2008-02-22 02:30:36Z das */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
16 * See e_atanh.c for complete comments.
18 * Converted to long double by David Schultz <das@FreeBSD.ORG> and
29 #include "math_private.h"
31 /* EXP_TINY is the threshold below which we use atanh(x) ~= x. */
32 #if LDBL_MANT_DIG == 64
34 #elif LDBL_MANT_DIG == 113
37 #error "Unsupported long double format"
40 #if LDBL_MAX_EXP != 0x4000
41 /* We also require the usual expsign encoding. */
42 #error "Unsupported long double format"
45 #define BIAS (LDBL_MAX_EXP - 1)
47 static const double one = 1.0, huge = 1e300;
48 static const double zero = 0.0;
57 GET_LDBL_EXPSIGN(hx, x);
59 if (ix >= 0x3fff) /* |x| >= 1, or NaN or misnormal */
60 RETURNI(fabsl(x) == 1 ? x / zero : (x - x) / (x - x));
61 if (ix < BIAS + EXP_TINY && (huge + x) > zero)
62 RETURNI(x); /* x is tiny */
63 SET_LDBL_EXPSIGN(x, ix);
64 if (ix < 0x3ffe) { /* |x| < 0.5, or misnormal */
66 t = 0.5*log1pl(t+t*x/(one-x));
68 t = 0.5*log1pl((x+x)/(one-x));
69 RETURNI((hx & 0x8000) == 0 ? t : -t);