1 files changed, 12 insertions, 0 deletions
diff --git a/circuitpython/lib/libm_dbl/tanh.c b/circuitpython/lib/libm_dbl/tanh.c
new file mode 100644
index 0000000..6bdb7c3
--- /dev/null
+++ b/circuitpython/lib/libm_dbl/tanh.c
@@ -0,0 +1,12 @@
+#include <math.h>
+
+double tanh(double x) {
+    int sign = 0;
+    if (x < 0) {
+        sign = 1;
+        x = -x;
+    }
+    x = expm1(-2 * x);
+    x = x / (x + 2);
+    return sign ? x : -x;
+}