s_tanhf.c revision 2116 
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[] = "$Id: s_tanhf.c,v 1.2 1994/08/18 23:10:23 jtc Exp $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23#ifdef __STDC__
24static const float one=1.0, two=2.0, tiny = 1.0e-30;
25#else
26static float one=1.0, two=2.0, tiny = 1.0e-30;
27#endif
28
29#ifdef __STDC__
30	float tanhf(float x)
31#else
32	float tanhf(x)
33	float x;
34#endif
35{
36	float t,z;
37	int32_t jx,ix;
38
39	GET_FLOAT_WORD(jx,x);
40	ix = jx&0x7fffffff;
41
42    /* x is INF or NaN */
43	if(ix>=0x7f800000) {
44	    if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
45	    else       return one/x-one;    /* tanh(NaN) = NaN */
46	}
47
48    /* |x| < 22 */
49	if (ix < 0x41b00000) {		/* |x|<22 */
50	    if (ix<0x24000000) 		/* |x|<2**-55 */
51		return x*(one+x);    	/* tanh(small) = small */
52	    if (ix>=0x3f800000) {	/* |x|>=1  */
53		t = expm1f(two*fabsf(x));
54		z = one - two/(t+two);
55	    } else {
56	        t = expm1f(-two*fabsf(x));
57	        z= -t/(t+two);
58	    }
59    /* |x| > 22, return +-1 */
60	} else {
61	    z = one - tiny;		/* raised inexact flag */
62	}
63	return (jx>=0)? z: -z;
64}
65