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 * ====================================================
15 #include <sys/cdefs.h>
17 * See e_atanh.c for complete comments.
19 * Converted to long double by David Schultz <das@FreeBSD.ORG> and
30 #include "math_private.h"
32 /* EXP_TINY is the threshold below which we use atanh(x) ~= x. */
33 #if LDBL_MANT_DIG == 64
35 #elif LDBL_MANT_DIG == 113
38 #error "Unsupported long double format"
41 #if LDBL_MAX_EXP != 0x4000
42 /* We also require the usual expsign encoding. */
43 #error "Unsupported long double format"
46 #define BIAS (LDBL_MAX_EXP - 1)
48 static const double one = 1.0, huge = 1e300;
49 static const double zero = 0.0;
58 GET_LDBL_EXPSIGN(hx, x);
60 if (ix >= 0x3fff) /* |x| >= 1, or NaN or misnormal */
61 RETURNI(fabsl(x) == 1 ? x / zero : (x - x) / (x - x));
62 if (ix < BIAS + EXP_TINY && (huge + x) > zero)
63 RETURNI(x); /* x is tiny */
64 SET_LDBL_EXPSIGN(x, ix);
65 if (ix < 0x3ffe) { /* |x| < 0.5, or misnormal */
67 t = 0.5*log1pl(t+t*x/(one-x));
69 t = 0.5*log1pl((x+x)/(one-x));
70 RETURNI((hx & 0x8000) == 0 ? t : -t);