1 files changed, 67 insertions, 0 deletions
diff --git a/src/pkg/math/tan.go b/src/pkg/math/tan.go
new file mode 100644
index 000000000..2d4a044b8
--- /dev/null
+++ b/src/pkg/math/tan.go
@@ -0,0 +1,67 @@
+// 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
+
+import "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) {
+			panic(NaN());
+		}
+		temp = 1/temp;
+	}
+	if sign {
+		temp = -temp;
+	}
+	return temp;
+}