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/* @(#)s_tanh.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */
 
#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
#endif
 
/* Tanh(x)
 * Return the Hyperbolic Tangent of x
 *
 * Method :
 *                                     x    -x
 *                                    e  - e
 *      0. tanh(x) is defined to be -----------
 *                                     x    -x
 *                                    e  + e
 *      1. reduce x to non-negative by tanh(-x) = -tanh(x).
 *      2.  0      <= x <= 2**-55 : tanh(x) := x*(one+x)
 *                                              -t
 *          2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)
 *                                             t + 2
 *                                                   2
 *          1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)
 *                                                 t + 2
 *          22.0   <  x <= INF    : tanh(x) := 1.
 *
 * Special cases:
 *      tanh(NaN) is NaN;
 *      only tanh(0)=0 is exact for finite argument.
 */
 
#include "math.h"
#include "math_private.h"
 
#ifdef __STDC__
static const double one=1.0, two=2.0, tiny = 1.0e-300;
#else
static double one=1.0, two=2.0, tiny = 1.0e-300;
#endif
 
#ifdef __STDC__
        double tanh(double x)
#else
        double tanh(x)
        double x;
#endif
{
        double t,z;
        int32_t jx,ix;
 
    /* High word of |x|. */
        GET_HIGH_WORD(jx,x);
        ix = jx&0x7fffffff;
 
    /* x is INF or NaN */
        if(ix>=0x7ff00000) {
            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
            else       return one/x-one;    /* tanh(NaN) = NaN */
        }
 
    /* |x| < 22 */
        if (ix < 0x40360000) {          /* |x|<22 */
            if (ix<0x3c800000)          /* |x|<2**-55 */
                return x*(one+x);       /* tanh(small) = small */
            if (ix>=0x3ff00000) {       /* |x|>=1  */
                t = expm1(two*fabs(x));
                z = one - two/(t+two);
            } else {
                t = expm1(-two*fabs(x));
                z= -t/(t+two);
            }
    /* |x| > 22, return +-1 */
        } else {
            z = one - tiny;             /* raised inexact flag */
        }
        return (jx>=0)? z: -z;
}

Line No.	Rev	Author	Line
1	1325	phoenix	`/* @(#)s_tanh.c 5.1 93/09/24 */`
2			`/*`
3			`* ====================================================`
4			`* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.`
5			`*`
6			`* Developed at SunPro, a Sun Microsystems, Inc. business.`
7			`* Permission to use, copy, modify, and distribute this`
8			`* software is freely granted, provided that this notice`
9			`* is preserved.`
10			`* ====================================================`
11			`*/`
12
13			`#if defined(LIBM_SCCS) && !defined(lint)`
14			`static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";`
15			`#endif`
16
17			`/* Tanh(x)`
18			`* Return the Hyperbolic Tangent of x`
19			`*`
20			`* Method :`
21			`* x -x`
22			`* e - e`
23			`* 0. tanh(x) is defined to be -----------`
24			`* x -x`
25			`* e + e`
26			`* 1. reduce x to non-negative by tanh(-x) = -tanh(x).`
27			`* 2. 0 <= x <= 2*-55 : tanh(x) := x(one+x)`
28			`* -t`
29			`* 2**-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x)`
30			`* t + 2`
31			`* 2`
32			`* 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x)`
33			`* t + 2`
34			`* 22.0 < x <= INF : tanh(x) := 1.`
35			`*`
36			`* Special cases:`
37			`* tanh(NaN) is NaN;`
38			`* only tanh(0)=0 is exact for finite argument.`
39			`*/`
40
41			`#include "math.h"`
42			`#include "math_private.h"`
43
44			`#ifdef __STDC__`
45			`static const double one=1.0, two=2.0, tiny = 1.0e-300;`
46			`#else`
47			`static double one=1.0, two=2.0, tiny = 1.0e-300;`
48			`#endif`
49
50			`#ifdef __STDC__`
51			`double tanh(double x)`
52			`#else`
53			`double tanh(x)`
54			`double x;`
55			`#endif`
56			`{`
57			`double t,z;`
58			`int32_t jx,ix;`
59
60			`/* High word of \|x\|. */`
61			`GET_HIGH_WORD(jx,x);`
62			`ix = jx&0x7fffffff;`
63
64			`/* x is INF or NaN */`
65			`if(ix>=0x7ff00000) {`
66			`if (jx>=0) return one/x+one; /* tanh(+-inf)=+-1 */`
67			`else return one/x-one; /* tanh(NaN) = NaN */`
68			`}`
69
70			`/* \|x\| < 22 */`
71			`if (ix < 0x40360000) { /* \|x\|<22 */`
72			`if (ix<0x3c800000) /* \|x\|<2*-55 /`
73			`return x(one+x); / tanh(small) = small */`
74			`if (ix>=0x3ff00000) { /* \|x\|>=1 */`
75			`t = expm1(two*fabs(x));`
76			`z = one - two/(t+two);`
77			`} else {`
78			`t = expm1(-two*fabs(x));`
79			`z= -t/(t+two);`
80			`}`
81			`/* \|x\| > 22, return +-1 */`
82			`} else {`
83			`z = one - tiny; /* raised inexact flag */`
84			`}`
85			`return (jx>=0)? z: -z;`
86			`}`

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[/] [or1k/] [trunk/] [linux/] [uClibc/] [libm/] [s_tanh.c] - Blame information for rev 1325