Add a "fork" of musl as //fusl.

fusl/src/math/tanhl.c

Index: fusl/src/math/tanhl.c
diff --git a/fusl/src/math/tanhl.c b/fusl/src/math/tanhl.c
new file mode 100644
index 0000000000000000000000000000000000000000..4e1aa9f87dde30bc14f43bed200fe2a968e45108
--- /dev/null
+++ b/fusl/src/math/tanhl.c
@@ -0,0 +1,48 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double tanhl(long double x)
+{
+	return tanh(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+long double tanhl(long double x)
+{
+	union ldshape u = {x};
+	unsigned ex = u.i.se & 0x7fff;
+	unsigned sign = u.i.se & 0x8000;
+	uint32_t w;
+	long double t;
+
+	/* x = |x| */
+	u.i.se = ex;
+	x = u.f;
+	w = u.i.m >> 32;
+
+	if (ex > 0x3ffe || (ex == 0x3ffe && w > 0x8c9f53d5)) {
+		/* |x| > log(3)/2 ~= 0.5493 or nan */
+		if (ex >= 0x3fff+5) {
+			/* |x| >= 32 */
+			t = 1 + 0/(x + 0x1p-120f);
+		} else {
+			t = expm1l(2*x);
+			t = 1 - 2/(t+2);
+		}
+	} else if (ex > 0x3ffd || (ex == 0x3ffd && w > 0x82c577d4)) {
+		/* |x| > log(5/3)/2 ~= 0.2554 */
+		t = expm1l(2*x);
+		t = t/(t+2);
+	} else {
+		/* |x| is small */
+		t = expm1l(-2*x);
+		t = -t/(t+2);
+	}
+	return sign ? -t : t;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double tanhl(long double x)
+{
+	return tanh(x);
+}
+#endif