65 lines
1.1 KiB
Go
65 lines
1.1 KiB
Go
// 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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package math
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/*
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Floating point tangent.
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*/
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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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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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flag := false
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sign := false
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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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x = x * (4 / Pi) /* overflow? */
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var e float64
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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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xsq := x * x
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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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if flag {
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if temp == 0 {
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return NaN()
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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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