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

fusl/src/math/tanl.c

Index: fusl/src/math/tanl.c
diff --git a/fusl/src/math/tanl.c b/fusl/src/math/tanl.c
new file mode 100644
index 0000000000000000000000000000000000000000..6af067127ade990b98d26696594e5737fbf50ade
--- /dev/null
+++ b/fusl/src/math/tanl.c
@@ -0,0 +1,29 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double tanl(long double x)
+{
+	return tan(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+long double tanl(long double x)
+{
+	union ldshape u = {x};
+	long double y[2];
+	unsigned n;
+
+	u.i.se &= 0x7fff;
+	if (u.i.se == 0x7fff)
+		return x - x;
+	if (u.f < M_PI_4) {
+		if (u.i.se < 0x3fff - LDBL_MANT_DIG/2) {
+			/* raise inexact if x!=0 and underflow if subnormal */
+			FORCE_EVAL(u.i.se == 0 ? x*0x1p-120f : x+0x1p120f);
+			return x;
+		}
+		return __tanl(x, 0, 0);
+	}
+	n = __rem_pio2l(x, y);
+	return __tanl(y[0], y[1], n&1);
+}
+#endif