2008-03-28 14:56:47 -06:00
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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2008-06-27 18:06:23 -06:00
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package math
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2008-03-28 14:56:47 -06:00
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2009-01-15 20:11:32 -07:00
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import "math"
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2008-03-28 14:56:47 -06:00
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/*
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2008-07-08 21:48:41 -06:00
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* floating point tangent
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2008-03-28 14:56:47 -06:00
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*/
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2009-03-05 14:31:01 -07:00
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// Tan returns the tangent of x.
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func Tan(x float64) float64 {
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// Coefficients are #4285 from Hart & Cheney. (19.74D)
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const
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(
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P0 = -.1306820264754825668269611177e+5;
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P1 = .1055970901714953193602353981e+4;
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P2 = -.1550685653483266376941705728e+2;
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P3 = .3422554387241003435328470489e-1;
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P4 = .3386638642677172096076369e-4;
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Q0 = -.1663895238947119001851464661e+5;
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Q1 = .4765751362916483698926655581e+4;
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Q2 = -.1555033164031709966900124574e+3;
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)
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2008-11-19 17:14:31 -07:00
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flag := false;
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sign := false;
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2008-03-28 14:56:47 -06:00
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if(x < 0) {
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x = -x;
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sign = true;
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}
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2009-01-15 20:11:32 -07:00
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x = x * (4/Pi); /* overflow? */
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var e float64;
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2009-01-22 17:23:44 -07:00
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e, x = Modf(x);
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i := int32(e);
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switch i & 3 {
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case 1:
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x = 1 - x;
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flag = true;
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case 2:
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sign = !sign;
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flag = true;
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case 3:
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x = 1 - x;
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sign = !sign;
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}
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2008-11-19 17:14:31 -07:00
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xsq := x*x;
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2009-01-15 20:11:32 -07:00
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temp := ((((P4*xsq+P3)*xsq+P2)*xsq+P1)*xsq+P0)*x;
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temp = temp/(((xsq+Q2)*xsq+Q1)*xsq+Q0);
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2008-03-28 14:56:47 -06:00
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if flag {
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if(temp == 0) {
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panic(NaN());
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2008-03-28 14:56:47 -06:00
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}
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temp = 1/temp;
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}
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if sign {
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temp = -temp;
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}
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return temp;
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}
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