85 lines
2.8 KiB
C#
85 lines
2.8 KiB
C#
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/*
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* Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/* tan(x)
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* Return tangent function of x.
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*
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* kernel function:
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* __kernel_tan ... tangent function on [-pi/4,pi/4]
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* __ieee754_rem_pio2 ... argument reduction routine
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*
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* Method.
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* Let S,C and T denote the sin, cos and tan respectively on
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* [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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* in [-pi/4 , +pi/4], and let n = k mod 4.
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* We have
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*
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* n sin(x) cos(x) tan(x)
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* ----------------------------------------------------------
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* 0 S C T
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* 1 C -S -1/T
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* 2 -S -C T
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* 3 -C S -1/T
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* ----------------------------------------------------------
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*
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* Special cases:
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* Let trig be any of sin, cos, or tan.
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* trig(+-INF) is NaN, with signals;
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* trig(NaN) is that NaN;
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*
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* Accuracy:
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* TRIG(x) returns trig(x) nearly rounded
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*/
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static partial class fdlibm
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{
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internal static
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double tan(double x)
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{
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double z=0.0;
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int n, ix;
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/* High word of x. */
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ix = __HI(x);
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/* |x| ~< pi/4 */
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ix &= 0x7fffffff;
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if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
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/* tan(Inf or NaN) is NaN */
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else if (ix>=0x7ff00000) return x-x; /* NaN */
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/* argument reduction needed */
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else {
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double y_0_ = 0.0, y_1_ = 0.0;
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n = __ieee754_rem_pio2(x, ref y_0_, ref y_1_);
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return __kernel_tan(y_0_,y_1_,1-((n&1)<<1)); /* 1 -- n even
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-1 -- n odd */
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}
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}
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}
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