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

fusl/src/math/modfl.c

Index: fusl/src/math/modfl.c
diff --git a/fusl/src/math/modfl.c b/fusl/src/math/modfl.c
new file mode 100644
index 0000000000000000000000000000000000000000..a47b1924f75d1125b712e3ccf5b0f39af27fd8f2
--- /dev/null
+++ b/fusl/src/math/modfl.c
@@ -0,0 +1,53 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double modfl(long double x, long double *iptr)
+{
+	double d;
+	long double r;
+
+	r = modf(x, &d);
+	*iptr = d;
+	return r;
+}
+#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+
+static const long double toint = 1/LDBL_EPSILON;
+
+long double modfl(long double x, long double *iptr)
+{
+	union ldshape u = {x};
+	int e = (u.i.se & 0x7fff) - 0x3fff;
+	int s = u.i.se >> 15;
+	long double absx;
+	long double y;
+
+	/* no fractional part */
+	if (e >= LDBL_MANT_DIG-1) {
+		*iptr = x;
+		if (isnan(x))
+			return x;
+		return s ? -0.0 : 0.0;
+	}
+
+	/* no integral part*/
+	if (e < 0) {
+		*iptr = s ? -0.0 : 0.0;
+		return x;
+	}
+
+	/* raises spurious inexact */
+	absx = s ? -x : x;
+	y = absx + toint - toint - absx;
+	if (y == 0) {
+		*iptr = x;
+		return s ? -0.0 : 0.0;
+	}
+	if (y > 0)
+		y -= 1;
+	if (s)
+		y = -y;
+	*iptr = x + y;
+	return -y;
+}
+#endif