1 files changed, 25 insertions, 0 deletions
diff --git a/src/base/math/tanh.c b/src/base/math/tanh.c
new file mode 100644
index 0000000..81e428a
--- /dev/null
+++ b/src/base/math/tanh.c
@@ -0,0 +1,25 @@
+#include <u.h>
+#include <base.h>
+
+/*
+	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.
+ */
+
+double
+math·tanh(double arg)
+{
+
+	if(arg < 0) {
+		arg = -arg;
+		if(arg > 21)
+			return -1;
+		return -math·sinh(arg)/math·cosh(arg);
+	}
+	if(arg > 21)
+		return 1;
+	return math·sinh(arg)/math·cosh(arg);
+}