1/* s_tanhl.c -- long double version of s_tanh.c.
2 * Conversion to long double by Ulrich Drepper,
3 * Cygnus Support, drepper@cygnus.com.
4 */
5
6/*
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 *
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
13 * is preserved.
14 * ====================================================
15 */
16
17/* Changes for 128-bit long double contributed by
18 Stephen L. Moshier <moshier@na-net.ornl.gov> */
19
20/* tanhl(x)
21 * Return the Hyperbolic Tangent of x
22 *
23 * Method :
24 * x -x
25 * e - e
26 * 0. tanhl(x) is defined to be -----------
27 * x -x
28 * e + e
29 * 1. reduce x to non-negative by tanhl(-x) = -tanhl(x).
30 * 2. 0 <= x <= 2**-57 : tanhl(x) := x*(one+x)
31 * -t
32 * 2**-57 < x <= 1 : tanhl(x) := -----; t = expm1l(-2x)
33 * t + 2
34 * 2
35 * 1 <= x <= 40.0 : tanhl(x) := 1- ----- ; t=expm1l(2x)
36 * t + 2
37 * 40.0 < x <= INF : tanhl(x) := 1.
38 *
39 * Special cases:
40 * tanhl(NaN) is NaN;
41 * only tanhl(0)=0 is exact for finite argument.
42 */
43
44#include <float.h>
45#include <math.h>
46#include <math_private.h>
47#include <libm-alias-ldouble.h>
48
49static const _Float128 one = 1.0, two = 2.0, tiny = L(1.0e-4900);
50
51_Float128
52__tanhl (_Float128 x)
53{
54 _Float128 t, z;
55 uint32_t jx, ix;
56 ieee854_long_double_shape_type u;
57
58 /* Words of |x|. */
59 u.value = x;
60 jx = u.parts32.w0;
61 ix = jx & 0x7fffffff;
62 /* x is INF or NaN */
63 if (ix >= 0x7fff0000)
64 {
65 /* for NaN it's not important which branch: tanhl(NaN) = NaN */
66 if (jx & 0x80000000)
67 return one / x - one; /* tanhl(-inf)= -1; */
68 else
69 return one / x + one; /* tanhl(+inf)=+1 */
70 }
71
72 /* |x| < 40 */
73 if (ix < 0x40044000)
74 {
75 if (u.value == 0)
76 return x; /* x == +- 0 */
77 if (ix < 0x3fc60000) /* |x| < 2^-57 */
78 {
79 math_check_force_underflow (x);
80 return x * (one + tiny); /* tanh(small) = small */
81 }
82 u.parts32.w0 = ix; /* Absolute value of x. */
83 if (ix >= 0x3fff0000)
84 { /* |x| >= 1 */
85 t = __expm1l (two * u.value);
86 z = one - two / (t + two);
87 }
88 else
89 {
90 t = __expm1l (-two * u.value);
91 z = -t / (t + two);
92 }
93 /* |x| > 40, return +-1 */
94 }
95 else
96 {
97 z = one - tiny; /* raised inexact flag */
98 }
99 return (jx & 0x80000000) ? -z : z;
100}
101libm_alias_ldouble (__tanh, tanh)
102