1 files changed, 65 insertions, 0 deletions
diff --git a/libgo/go/math/tan.go b/libgo/go/math/tan.go
new file mode 100644
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+++ b/libgo/go/math/tan.go
@@ -0,0 +1,65 @@
+// 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
+}