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 }
55