1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
2 *
3 * ***** BEGIN LICENSE BLOCK *****
4 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
5 *
6 * The contents of this file are subject to the Mozilla Public License Version
7 * 1.1 (the "License"); you may not use this file except in compliance with
8 * the License. You may obtain a copy of the License at
9 * http://www.mozilla.org/MPL/
10 *
11 * Software distributed under the License is distributed on an "AS IS" basis,
12 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
13 * for the specific language governing rights and limitations under the
14 * License.
15 *
16 * The Original Code is Mozilla Communicator client code, released
17 * March 31, 1998.
18 *
19 * The Initial Developer of the Original Code is
20 * Sun Microsystems, Inc.
21 * Portions created by the Initial Developer are Copyright (C) 1998
22 * the Initial Developer. All Rights Reserved.
23 *
24 * Contributor(s):
25 *
26 * Alternatively, the contents of this file may be used under the terms of
27 * either of the GNU General Public License Version 2 or later (the "GPL"),
28 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
29 * in which case the provisions of the GPL or the LGPL are applicable instead
30 * of those above. If you wish to allow use of your version of this file only
31 * under the terms of either the GPL or the LGPL, and not to allow others to
32 * use your version of this file under the terms of the MPL, indicate your
33 * decision by deleting the provisions above and replace them with the notice
34 * and other provisions required by the GPL or the LGPL. If you do not delete
35 * the provisions above, a recipient may use your version of this file under
36 * the terms of any one of the MPL, the GPL or the LGPL.
37 *
38 * ***** END LICENSE BLOCK ***** */
40 /* @(#)s_tan.c 1.3 95/01/18 */
41 /*
42 * ====================================================
43 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
44 *
45 * Developed at SunSoft, a Sun Microsystems, Inc. business.
46 * Permission to use, copy, modify, and distribute this
47 * software is freely granted, provided that this notice
48 * is preserved.
49 * ====================================================
50 */
52 /* tan(x)
53 * Return tangent function of x.
54 *
55 * kernel function:
56 * __kernel_tan ... tangent function on [-pi/4,pi/4]
57 * __ieee754_rem_pio2 ... argument reduction routine
58 *
59 * Method.
60 * Let S,C and T denote the sin, cos and tan respectively on
61 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
62 * in [-pi/4 , +pi/4], and let n = k mod 4.
63 * We have
64 *
65 * n sin(x) cos(x) tan(x)
66 * ----------------------------------------------------------
67 * 0 S C T
68 * 1 C -S -1/T
69 * 2 -S -C T
70 * 3 -C S -1/T
71 * ----------------------------------------------------------
72 *
73 * Special cases:
74 * Let trig be any of sin, cos, or tan.
75 * trig(+-INF) is NaN, with signals;
76 * trig(NaN) is that NaN;
77 *
78 * Accuracy:
79 * TRIG(x) returns trig(x) nearly rounded
80 */
82 #include "fdlibm.h"
84 #ifdef __STDC__
85 double fd_tan(double x)
86 #else
87 double fd_tan(x)
88 double x;
89 #endif
90 {
91 fd_twoints u;
92 double y[2],z=0.0;
93 int n, ix;
95 /* High word of x. */
96 u.d = x;
97 ix = __HI(u);
99 /* |x| ~< pi/4 */
100 ix &= 0x7fffffff;
101 if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
103 /* tan(Inf or NaN) is NaN */
104 else if (ix>=0x7ff00000) return x-x; /* NaN */
106 /* argument reduction needed */
107 else {
108 n = __ieee754_rem_pio2(x,y);
109 return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even
110 -1 -- n odd */
111 }
112 }