s_tanhf.c revision a0ee07829a9ba7e99ef68e8c12551301cc797f0f 
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 <sys/cdefs.h>
17__FBSDID("$FreeBSD$");
18
19#include "math.h"
20#include "math_private.h"
21
22static const float one=1.0, two=2.0, tiny = 1.0e-30, huge = 1.0e30;
23float
24tanhf(float x)
25{
26	float t,z;
27	int32_t jx,ix;
28
29	GET_FLOAT_WORD(jx,x);
30	ix = jx&0x7fffffff;
31
32    /* x is INF or NaN */
33	if(ix>=0x7f800000) {
34	    if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
35	    else       return one/x-one;    /* tanh(NaN) = NaN */
36	}
37
38    /* |x| < 9 */
39	if (ix < 0x41100000) {		/* |x|<9 */
40	    if (ix<0x39800000) {	/* |x|<2**-12 */
41		if(huge+x>one) return x; /* tanh(tiny) = tiny with inexact */
42	    }
43	    if (ix>=0x3f800000) {	/* |x|>=1  */
44		t = expm1f(two*fabsf(x));
45		z = one - two/(t+two);
46	    } else {
47	        t = expm1f(-two*fabsf(x));
48	        z= -t/(t+two);
49	    }
50    /* |x| >= 9, return +-1 */
51	} else {
52	    z = one - tiny;		/* raise inexact flag */
53	}
54	return (jx>=0)? z: -z;
55}
56