1
2 /* @(#)z_tanf.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 * Tangent
11 *
12 * Input:
13 * x - floating point value
14 *
15 * Output:
16 * tangent of x
17 *
18 * Description:
19 * This routine calculates the tangent of x.
20 *
21 *****************************************************************/
22
23 #include "fdlibm.h"
24 #include "zmath.h"
25
26 static const float TWO_OVER_PI = 0.6366197723;
27 static const float p[] = { -0.958017723e-1 };
28 static const float q[] = { -0.429135777,
29 0.971685835e-2 };
30
31 float
32 _DEFUN (tanf, (float),
33 float x)
34 {
35 float y, f, g, XN, xnum, xden, res;
36 int N;
37
38 /* Check for special values. */
39 switch (numtestf (x))
40 {
41 case NAN:
42 errno = EDOM;
43 return (x);
44 case INF:
45 errno = EDOM;
46 return (z_notanum_f.f);
47 }
48
49 y = fabsf (x);
50
51 /* Check for values that are out of our range. */
52 if (y > 105414357.0)
53 {
54 errno = ERANGE;
55 return (y);
56 }
57
58 if (x < 0.0)
59 N = (int) (x * TWO_OVER_PI - 0.5);
60 else
61 N = (int) (x * TWO_OVER_PI + 0.5);
62
63 XN = (float) N;
64
65 f = x - N * __PI_OVER_TWO;
66
67 /* Check for values that are too small. */
68 if (-z_rooteps_f < f && f < z_rooteps_f)
69 {
70 xnum = f;
71 xden = 1.0;
72 }
73
74 /* Calculate the polynomial. */
75 else
76 {
77 g = f * f;
78
79 xnum = f * (p[0] * g) + f;
80 xden = (q[1] * g + q[0]) * g + 1.0;
81 }
82
83 /* Check for odd or even values. */
84 if (N & 1)
85 {
86 xnum = -xnum;
87 res = xden / xnum;
88 }
89 else
90 {
91 res = xnum / xden;
92 }
93
94 return (res);
95 }
96
97 #ifdef _DOUBLE_IS_32BITS
98
tan(double x)99 double tan (double x)
100 {
101 return (double) tanf ((float) x);
102 }
103
104 #endif /* _DOUBLE_IS_32BITS */
105