1 files changed, 42 insertions, 0 deletions
diff --git a/lib/libm/tanhf.c b/lib/libm/tanhf.c
new file mode 100644
index 00000000..f4ae759d
--- /dev/null
+++ b/lib/libm/tanhf.c
@@ -0,0 +1,42 @@
+#include "libm.h"
+
+float tanhf(float x)
+{
+	union {
+		float f;
+		uint32_t i;
+	} u = { .f = x };
+	uint32_t w;
+	int sign;
+	float t;
+
+	/* x = |x| */
+	sign = u.i >> 31;
+	u.i &= 0x7fffffff;
+	x = u.f;
+	w = u.i;
+
+	if (w > 0x3f0c9f54) {
+		/* |x| > log(3)/2 ~= 0.5493 or nan */
+		if (w > 0x41200000) {
+			/* |x| > 10 */
+			t = 1 + 0 / x;
+		} else {
+			t = expm1f(2 * x);
+			t = 1 - 2 / (t + 2);
+		}
+	} else if (w > 0x3e82c578) {
+		/* |x| > log(5/3)/2 ~= 0.2554 */
+		t = expm1f(2 * x);
+		t = t / (t + 2);
+	} else if (w >= 0x00800000) {
+		/* |x| >= 0x1p-126 */
+		t = expm1f(-2 * x);
+		t = -t / (t + 2);
+	} else {
+		/* |x| is subnormal */
+		FORCE_EVAL(x * x);
+		t = x;
+	}
+	return sign ? -t : t;
+}