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

fusl/src/math/roundl.c

Index: fusl/src/math/roundl.c
diff --git a/fusl/src/math/roundl.c b/fusl/src/math/roundl.c
new file mode 100644
index 0000000000000000000000000000000000000000..f4ff6820a982276321f6bfe8198e0975c7016017
--- /dev/null
+++ b/fusl/src/math/roundl.c
@@ -0,0 +1,37 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double roundl(long double x)
+{
+	return round(x);
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+
+static const long double toint = 1/LDBL_EPSILON;
+
+long double roundl(long double x)
+{
+	union ldshape u = {x};
+	int e = u.i.se & 0x7fff;
+	long double y;
+
+	if (e >= 0x3fff+LDBL_MANT_DIG-1)
+		return x;
+	if (u.i.se >> 15)
+		x = -x;
+	if (e < 0x3fff-1) {
+		FORCE_EVAL(x + toint);
+		return 0*u.f;
+	}
+	y = x + toint - toint - x;
+	if (y > 0.5)
+		y = y + x - 1;
+	else if (y <= -0.5)
+		y = y + x + 1;
+	else
+		y = y + x;
+	if (u.i.se >> 15)
+		y = -y;
+	return y;
+}
+#endif