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