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lightning-sunbird  0.9+nobinonly
s_tan.c
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00001 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
00002  *
00003  * ***** BEGIN LICENSE BLOCK *****
00004  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
00005  *
00006  * The contents of this file are subject to the Mozilla Public License Version
00007  * 1.1 (the "License"); you may not use this file except in compliance with
00008  * the License. You may obtain a copy of the License at
00009  * http://www.mozilla.org/MPL/
00010  *
00011  * Software distributed under the License is distributed on an "AS IS" basis,
00012  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
00013  * for the specific language governing rights and limitations under the
00014  * License.
00015  *
00016  * The Original Code is Mozilla Communicator client code, released
00017  * March 31, 1998.
00018  *
00019  * The Initial Developer of the Original Code is
00020  * Sun Microsystems, Inc.
00021  * Portions created by the Initial Developer are Copyright (C) 1998
00022  * the Initial Developer. All Rights Reserved.
00023  *
00024  * Contributor(s):
00025  *
00026  * Alternatively, the contents of this file may be used under the terms of
00027  * either of the GNU General Public License Version 2 or later (the "GPL"),
00028  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
00029  * in which case the provisions of the GPL or the LGPL are applicable instead
00030  * of those above. If you wish to allow use of your version of this file only
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00032  * use your version of this file under the terms of the MPL, indicate your
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00035  * the provisions above, a recipient may use your version of this file under
00036  * the terms of any one of the MPL, the GPL or the LGPL.
00037  *
00038  * ***** END LICENSE BLOCK ***** */
00039 
00040 /* @(#)s_tan.c 1.3 95/01/18 */
00041 /*
00042  * ====================================================
00043  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
00044  *
00045  * Developed at SunSoft, a Sun Microsystems, Inc. business.
00046  * Permission to use, copy, modify, and distribute this
00047  * software is freely granted, provided that this notice 
00048  * is preserved.
00049  * ====================================================
00050  */
00051 
00052 /* tan(x)
00053  * Return tangent function of x.
00054  *
00055  * kernel function:
00056  *     __kernel_tan         ... tangent function on [-pi/4,pi/4]
00057  *     __ieee754_rem_pio2   ... argument reduction routine
00058  *
00059  * Method.
00060  *      Let S,C and T denote the sin, cos and tan respectively on 
00061  *     [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 
00062  *     in [-pi/4 , +pi/4], and let n = k mod 4.
00063  *     We have
00064  *
00065  *          n        sin(x)      cos(x)        tan(x)
00066  *     ----------------------------------------------------------
00067  *         0         S         C           T
00068  *         1         C        -S          -1/T
00069  *         2        -S        -C           T
00070  *         3        -C         S          -1/T
00071  *     ----------------------------------------------------------
00072  *
00073  * Special cases:
00074  *      Let trig be any of sin, cos, or tan.
00075  *      trig(+-INF)  is NaN, with signals;
00076  *      trig(NaN)    is that NaN;
00077  *
00078  * Accuracy:
00079  *     TRIG(x) returns trig(x) nearly rounded 
00080  */
00081 
00082 #include "fdlibm.h"
00083 
00084 #ifdef __STDC__
00085        double fd_tan(double x)
00086 #else
00087        double fd_tan(x)
00088        double x;
00089 #endif
00090 {
00091         fd_twoints u;
00092        double y[2],z=0.0;
00093        int n, ix;
00094 
00095     /* High word of x. */
00096         u.d = x;
00097        ix = __HI(u);
00098 
00099     /* |x| ~< pi/4 */
00100        ix &= 0x7fffffff;
00101        if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
00102 
00103     /* tan(Inf or NaN) is NaN */
00104        else if (ix>=0x7ff00000) return x-x;             /* NaN */
00105 
00106     /* argument reduction needed */
00107        else {
00108            n = __ieee754_rem_pio2(x,y);
00109            return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even
00110                                                  -1 -- n odd */
00111        }
00112 }