1 /* from: FreeBSD: head/lib/msun/src/e_atanh.c 176451 2008-02-22 02:30:36Z das */
2
3 /*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
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
10 * is preserved.
11 * ====================================================
12 *
13 */
14
15 /*
16 * See e_atanh.c for complete comments.
17 *
18 * Converted to long double by David Schultz <das@FreeBSD.ORG> and
19 * Bruce D. Evans.
20 */
21
22 #include <float.h>
23 #ifdef __i386__
24 #include <ieeefp.h>
25 #endif
26
27 #include "fpmath.h"
28 #include "math.h"
29 #include "math_private.h"
30
31 /* EXP_TINY is the threshold below which we use atanh(x) ~= x. */
32 #if LDBL_MANT_DIG == 64
33 #define EXP_TINY -34
34 #elif LDBL_MANT_DIG == 113
35 #define EXP_TINY -58
36 #else
37 #error "Unsupported long double format"
38 #endif
39
40 #if LDBL_MAX_EXP != 0x4000
41 /* We also require the usual expsign encoding. */
42 #error "Unsupported long double format"
43 #endif
44
45 #define BIAS (LDBL_MAX_EXP - 1)
46
47 static const double one = 1.0, huge = 1e300;
48 static const double zero = 0.0;
49
50 long double
atanhl(long double x)51 atanhl(long double x)
52 {
53 long double t;
54 uint16_t hx, ix;
55
56 ENTERI();
57 GET_LDBL_EXPSIGN(hx, x);
58 ix = hx & 0x7fff;
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 */
65 t = x+x;
66 t = 0.5*log1pl(t+t*x/(one-x));
67 } else
68 t = 0.5*log1pl((x+x)/(one-x));
69 RETURNI((hx & 0x8000) == 0 ? t : -t);
70 }
71