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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.
*/
// Tan returns the tangent of x.
func Tan(x float64) float64 {
// 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
)
flag := false
sign := false
if x < 0 {
x = -x
sign = true
}
x = x * (4 / Pi) /* overflow? */
var e float64
e, x = 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 {
return NaN()
}
temp = 1 / temp
}
if sign {
temp = -temp
}
return temp
}
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