s_tanhf.c revision 153302 
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 153302 2005-12-11 11:40:55Z bde $";
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, huge = 1.0e30;
24float
25tanhf(float x)
26{
27	float t,z;
28	int32_t jx,ix;
29
30	GET_FLOAT_WORD(jx,x);
31	ix = jx&0x7fffffff;
32
33    /* x is INF or NaN */
34	if(ix>=0x7f800000) {
35	    if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
36	    else       return one/x-one;    /* tanh(NaN) = NaN */
37	}
38
39    /* |x| < 9 */
40	if (ix < 0x41100000) {		/* |x|<9 */
41	    if (ix<0x39800000) {	/* |x|<2**-12 */
42		if(huge+x>one) return x; /* tanh(tiny) = tiny with inexact */
43	    }
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| >= 9, return +-1 */
52	} else {
53	    z = one - tiny;		/* raise inexact flag */
54	}
55	return (jx>=0)? z: -z;
56}
57