1 files changed, 46 insertions, 0 deletions
diff --git a/src/pkg/math/asin.go b/src/pkg/math/asin.go
new file mode 100644
index 000000000..23c9a1069
--- /dev/null
+++ b/src/pkg/math/asin.go
@@ -0,0 +1,46 @@
+// 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"
+
+/*
+ * asin(arg) and acos(arg) return the arcsin, arccos,
+ * respectively of their arguments.
+ *
+ * Arctan is called after appropriate range reduction.
+ */
+
+// Asin returns the arc sine of x.
+func Asin(x float64) float64 {
+	sign := false;
+	if x < 0 {
+		x = -x;
+		sign = true;
+	}
+	if x > 1 {
+		return NaN();
+	}
+
+	temp := Sqrt(1 - x*x);
+	if x > 0.7 {
+		temp = Pi/2 - Atan(temp/x);
+	} else {
+		temp = Atan(x/temp);
+	}
+
+	if sign {
+		temp = -temp;
+	}
+	return temp;
+}
+
+// Acos returns the arc cosine of x.
+func Acos(x float64) float64 {
+	if x > 1 || x < -1 {
+		return NaN();
+	}
+	return Pi/2 - Asin(x);
+}