1 files changed, 28 insertions, 0 deletions
diff --git a/src/pkg/math/atan2.go b/src/pkg/math/atan2.go
new file mode 100644
index 000000000..72f2117b3
--- /dev/null
+++ b/src/pkg/math/atan2.go
@@ -0,0 +1,28 @@
+// 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"
+
+// Atan returns the arc tangent of y/x, using
+// the signs of the two to determine the quadrant
+// of the return value.
+func Atan2(x, y float64) float64 {
+	// Determine the quadrant and call atan.
+	if x+y == x {
+		if x >= 0 {
+			return Pi/2;
+		}
+		return -Pi/2;
+	}
+	q := Atan(x/y);
+	if y < 0 {
+		if q <= 0 {
+			return q + Pi;
+		}
+		return q - Pi;
+	}
+	return q;
+}