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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
/*
* floating point tangent
* Coefficients are #4285 from Hart & Cheney. (19.74D)
*/
const
(
p0 = -.1306820264754825668269611177e+5;
p1 = .1055970901714953193602353981e+4;
p2 = -.1550685653483266376941705728e+2;
p3 = .3422554387241003435328470489e-1;
p4 = .3386638642677172096076369e-4;
q0 = -.1663895238947119001851464661e+5;
q1 = .4765751362916483698926655581e+4;
q2 = -.1555033164031709966900124574e+3;
piu4 = .1273239544735162686151070107e+1; // 4/pi
)
export func Tan(arg float64) float64 {
flag := false;
sign := false;
x := arg;
if(x < 0) {
x = -x;
sign = true;
}
x = x * piu4; /* overflow? */
var e float64;
e, x = sys.modf(x);
i := int32(e);
switch i & 3 {
case 1:
x = 1 - x;
flag = true;
case 2:
sign = !sign;
flag = true;
case 3:
x = 1 - x;
sign = !sign;
}
xsq := x*x;
temp := ((((p4*xsq+p3)*xsq+p2)*xsq+p1)*xsq+p0)*x;
temp = temp/(((xsq+q2)*xsq+q1)*xsq+q0);
if flag {
if(temp == 0) {
panic(sys.NaN());
}
temp = 1/temp;
}
if sign {
temp = -temp;
}
return temp;
}
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