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

fusl/src/math/rintl.c

Index: fusl/src/math/rintl.c
diff --git a/fusl/src/math/rintl.c b/fusl/src/math/rintl.c
new file mode 100644
index 0000000000000000000000000000000000000000..374327db2282d450ceb79e12286db767eb452148
--- /dev/null
+++ b/fusl/src/math/rintl.c
@@ -0,0 +1,29 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double rintl(long double x)
+{
+	return rint(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+
+static const long double toint = 1/LDBL_EPSILON;
+
+long double rintl(long double x)
+{
+	union ldshape u = {x};
+	int e = u.i.se & 0x7fff;
+	int s = u.i.se >> 15;
+	long double y;
+
+	if (e >= 0x3fff+LDBL_MANT_DIG-1)
+		return x;
+	if (s)
+		y = x - toint + toint;
+	else
+		y = x + toint - toint;
+	if (y == 0)
+		return 0*x;
+	return y;
+}
+#endif