1*05a0b428SJohn Marino /* s_tanhf.c -- float version of s_tanh.c.
2*05a0b428SJohn Marino * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3*05a0b428SJohn Marino */
4*05a0b428SJohn Marino
5*05a0b428SJohn Marino /*
6*05a0b428SJohn Marino * ====================================================
7*05a0b428SJohn Marino * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8*05a0b428SJohn Marino *
9*05a0b428SJohn Marino * Developed at SunPro, a Sun Microsystems, Inc. business.
10*05a0b428SJohn Marino * Permission to use, copy, modify, and distribute this
11*05a0b428SJohn Marino * software is freely granted, provided that this notice
12*05a0b428SJohn Marino * is preserved.
13*05a0b428SJohn Marino * ====================================================
14*05a0b428SJohn Marino */
15*05a0b428SJohn Marino
16*05a0b428SJohn Marino #include "math.h"
17*05a0b428SJohn Marino #include "math_private.h"
18*05a0b428SJohn Marino
19*05a0b428SJohn Marino static const float one=1.0, two=2.0, tiny = 1.0e-30;
20*05a0b428SJohn Marino
21*05a0b428SJohn Marino float
tanhf(float x)22*05a0b428SJohn Marino tanhf(float x)
23*05a0b428SJohn Marino {
24*05a0b428SJohn Marino float t,z;
25*05a0b428SJohn Marino int32_t jx,ix;
26*05a0b428SJohn Marino
27*05a0b428SJohn Marino GET_FLOAT_WORD(jx,x);
28*05a0b428SJohn Marino ix = jx&0x7fffffff;
29*05a0b428SJohn Marino
30*05a0b428SJohn Marino /* x is INF or NaN */
31*05a0b428SJohn Marino if(ix>=0x7f800000) {
32*05a0b428SJohn Marino if (jx>=0) return one/x+one; /* tanh(+-inf)=+-1 */
33*05a0b428SJohn Marino else return one/x-one; /* tanh(NaN) = NaN */
34*05a0b428SJohn Marino }
35*05a0b428SJohn Marino
36*05a0b428SJohn Marino /* |x| < 22 */
37*05a0b428SJohn Marino if (ix < 0x41b00000) { /* |x|<22 */
38*05a0b428SJohn Marino if (ix == 0)
39*05a0b428SJohn Marino return x; /* x == +-0 */
40*05a0b428SJohn Marino if (ix<0x24000000) /* |x|<2**-55 */
41*05a0b428SJohn Marino return x*(one+x); /* tanh(small) = small */
42*05a0b428SJohn Marino if (ix>=0x3f800000) { /* |x|>=1 */
43*05a0b428SJohn Marino t = expm1f(two*fabsf(x));
44*05a0b428SJohn Marino z = one - two/(t+two);
45*05a0b428SJohn Marino } else {
46*05a0b428SJohn Marino t = expm1f(-two*fabsf(x));
47*05a0b428SJohn Marino z= -t/(t+two);
48*05a0b428SJohn Marino }
49*05a0b428SJohn Marino /* |x| > 22, return +-1 */
50*05a0b428SJohn Marino } else {
51*05a0b428SJohn Marino z = one - tiny; /* raised inexact flag */
52*05a0b428SJohn Marino }
53*05a0b428SJohn Marino return (jx>=0)? z: -z;
54*05a0b428SJohn Marino }
55