s_tanhf.c revision 97413 
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#ifndef lint
17static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_tanhf.c 97413 2002-05-28 18:15:04Z alfred $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static const float one=1.0, two=2.0, tiny = 1.0e-30;
24
25float
26tanhf(float x)
27{
28	float t,z;
29	int32_t jx,ix;
30
31	GET_FLOAT_WORD(jx,x);
32	ix = jx&0x7fffffff;
33
34    /* x is INF or NaN */
35	if(ix>=0x7f800000) {
36	    if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
37	    else       return one/x-one;    /* tanh(NaN) = NaN */
38	}
39
40    /* |x| < 22 */
41	if (ix < 0x41b00000) {		/* |x|<22 */
42	    if (ix<0x24000000) 		/* |x|<2**-55 */
43		return x*(one+x);    	/* tanh(small) = small */
44	    if (ix>=0x3f800000) {	/* |x|>=1  */
45		t = expm1f(two*fabsf(x));
46		z = one - two/(t+two);
47	    } else {
48	        t = expm1f(-two*fabsf(x));
49	        z= -t/(t+two);
50	    }
51    /* |x| > 22, return +-1 */
52	} else {
53	    z = one - tiny;		/* raised inexact flag */
54	}
55	return (jx>=0)? z: -z;
56}
57