1 files changed, 32 insertions, 0 deletions
diff --git a/src/lib/math/tanh.go b/src/lib/math/tanh.go
new file mode 100644
index 000000000..8d1748205
--- /dev/null
+++ b/src/lib/math/tanh.go
@@ -0,0 +1,32 @@
+// 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 tanh
+
+import		sinh "sinh"
+export		tanh
+
+/*
+	tanh(arg) computes the hyperbolic tangent of its floating
+	point argument.
+
+	sinh and cosh are called except for large arguments, which
+	would cause overflow improperly.
+ */
+
+func
+tanh(arg double) double
+{
+	if arg < 0 {
+		arg = -arg;
+		if arg > 21 {
+			return -1;
+		}
+		return -sinh.sinh(arg)/sinh.cosh(arg);
+	}
+	if arg > 21 {
+		return 1;
+	}
+	return sinh.sinh(arg)/sinh.cosh(arg);
+}