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/* @(#)z_tanh.c 1.0 98/08/13 */
/*****************************************************************
 * The following routines are coded directly from the algorithms
 * and coefficients given in "Software Manual for the Elementary
 * Functions" by William J. Cody, Jr. and William Waite, Prentice
 * Hall, 1980.
 *****************************************************************/
 
/*
 
FUNCTION
        <<tanh>>, <<tanhf>>---hyperbolic tangent
 
INDEX
tanh
INDEX
tanhf
 
ANSI_SYNOPSIS
        #include <math.h>
        double tanh(double <[x]>);
        float tanhf(float <[x]>);
 
TRAD_SYNOPSIS
        #include <math.h>
        double tanh(<[x]>)
        double <[x]>;
 
        float tanhf(<[x]>)
        float <[x]>;
 
 
DESCRIPTION
 
<<tanh>> computes the hyperbolic tangent of
the argument <[x]>.  Angles are specified in radians.
 
<<tanh(<[x]>)>> is defined as
. sinh(<[x]>)/cosh(<[x]>)
 
<<tanhf>> is identical, save that it takes and returns <<float>> values.
 
RETURNS
The hyperbolic tangent of <[x]> is returned.
 
PORTABILITY
<<tanh>> is ANSI C.  <<tanhf>> is an extension.
 
*/
 
/******************************************************************
 * Hyperbolic Tangent
 *
 * Input:
 *   x - floating point value
 *
 * Output:
 *   hyperbolic tangent of x
 *
 * Description:
 *   This routine calculates hyperbolic tangent.
 *
 *****************************************************************/
 
#include <float.h>
#include "fdlibm.h"
#include "zmath.h"
 
#ifndef _DOUBLE_IS_32BITS
 
static const double LN3_OVER2 = 0.54930614433405484570;
static const double p[] = { -0.16134119023996228053e+4,
                            -0.99225929672236083313e+2,
                            -0.96437492777225469787 };
static const double q[] = { 0.48402357071988688686e+4,
                            0.22337720718962312926e+4,
                            0.11274474380534949335e+3 };
 
double
_DEFUN (tanh, (double),
        double x)
{
  double f, res, g, P, Q, R;
 
  f = fabs (x);
 
  /* Check if the input is too big. */
  if (f > BIGX)
    res = 1.0;
 
  else if (f > LN3_OVER2)
    res = 1.0 - 2.0 / (exp (2 * f) + 1.0);
 
  /* Check if the input is too small. */
  else if (f < z_rooteps)
    res = f;
 
  /* Calculate the Taylor series. */
  else
    {
      g = f * f;
 
      P = (p[2] * g + p[1]) * g + p[0];
      Q = ((g + q[2]) * g + q[1]) * g + q[0];
      R = g * (P / Q);
 
      res = f + f * R;
    }
 
  if (x < 0.0)
    res = -res;
 
  return (res);
}
 
#endif /* _DOUBLE_IS_32BITS */

Line No.	Rev	Author	Line
1	56	joel
2			`/* @(#)z_tanh.c 1.0 98/08/13 */`
3			`/*****************************************************************`
4			`* The following routines are coded directly from the algorithms`
5			`* and coefficients given in "Software Manual for the Elementary`
6			`* Functions" by William J. Cody, Jr. and William Waite, Prentice`
7			`* Hall, 1980.`
8			`*****************************************************************/`
9
10			`/*`
11
12			`FUNCTION`
13			`<<tanh>>, <<tanhf>>---hyperbolic tangent`
14
15			`INDEX`
16			`tanh`
17			`INDEX`
18			`tanhf`
19
20			`ANSI_SYNOPSIS`
21			`#include <math.h>`
22			`double tanh(double <[x]>);`
23			`float tanhf(float <[x]>);`
24
25			`TRAD_SYNOPSIS`
26			`#include <math.h>`
27			`double tanh(<[x]>)`
28			`double <[x]>;`
29
30			`float tanhf(<[x]>)`
31			`float <[x]>;`
32
33
34			`DESCRIPTION`
35
36			`<<tanh>> computes the hyperbolic tangent of`
37			`the argument <[x]>. Angles are specified in radians.`
38
39			`<<tanh(<[x]>)>> is defined as`
40			`. sinh(<[x]>)/cosh(<[x]>)`
41
42			`<<tanhf>> is identical, save that it takes and returns <<float>> values.`
43
44			`RETURNS`
45			`The hyperbolic tangent of <[x]> is returned.`
46
47			`PORTABILITY`
48			`<<tanh>> is ANSI C. <<tanhf>> is an extension.`
49
50			`*/`
51
52			`/******************************************************************`
53			`* Hyperbolic Tangent`
54			`*`
55			`* Input:`
56			`* x - floating point value`
57			`*`
58			`* Output:`
59			`* hyperbolic tangent of x`
60			`*`
61			`* Description:`
62			`* This routine calculates hyperbolic tangent.`
63			`*`
64			`*****************************************************************/`
65
66			`#include <float.h>`
67			`#include "fdlibm.h"`
68			`#include "zmath.h"`
69
70			`#ifndef _DOUBLE_IS_32BITS`
71
72			`static const double LN3_OVER2 = 0.54930614433405484570;`
73			`static const double p[] = { -0.16134119023996228053e+4,`
74			`-0.99225929672236083313e+2,`
75			`-0.96437492777225469787 };`
76			`static const double q[] = { 0.48402357071988688686e+4,`
77			`0.22337720718962312926e+4,`
78			`0.11274474380534949335e+3 };`
79
80			`double`
81			`_DEFUN (tanh, (double),`
82			`double x)`
83			`{`
84			`double f, res, g, P, Q, R;`
85
86			`f = fabs (x);`
87
88			`/* Check if the input is too big. */`
89			`if (f > BIGX)`
90			`res = 1.0;`
91
92			`else if (f > LN3_OVER2)`
93			`res = 1.0 - 2.0 / (exp (2 * f) + 1.0);`
94
95			`/* Check if the input is too small. */`
96			`else if (f < z_rooteps)`
97			`res = f;`
98
99			`/* Calculate the Taylor series. */`
100			`else`
101			`{`
102			`g = f * f;`
103
104			`P = (p[2] * g + p[1]) * g + p[0];`
105			`Q = ((g + q[2]) * g + q[1]) * g + q[0];`
106			`R = g * (P / Q);`
107
108			`res = f + f * R;`
109			`}`
110
111			`if (x < 0.0)`
112			`res = -res;`
113
114			`return (res);`
115			`}`
116
117			`#endif /* _DOUBLE_IS_32BITS */`

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