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

fusl/src/math/ilogbl.c

Index: fusl/src/math/ilogbl.c
diff --git a/fusl/src/math/ilogbl.c b/fusl/src/math/ilogbl.c
new file mode 100644
index 0000000000000000000000000000000000000000..7b1a9cf8d007ff16c1d6fe072916a5a8a226e3e3
--- /dev/null
+++ b/fusl/src/math/ilogbl.c
@@ -0,0 +1,55 @@
+#include <limits.h>
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+int ilogbl(long double x)
+{
+	return ilogb(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+int ilogbl(long double x)
+{
+	#pragma STDC FENV_ACCESS ON
+	union ldshape u = {x};
+	uint64_t m = u.i.m;
+	int e = u.i.se & 0x7fff;
+
+	if (!e) {
+		if (m == 0) {
+			FORCE_EVAL(0/0.0f);
+			return FP_ILOGB0;
+		}
+		/* subnormal x */
+		for (e = -0x3fff+1; m>>63 == 0; e--, m<<=1);
+		return e;
+	}
+	if (e == 0x7fff) {
+		FORCE_EVAL(0/0.0f);
+		return m<<1 ? FP_ILOGBNAN : INT_MAX;
+	}
+	return e - 0x3fff;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+int ilogbl(long double x)
+{
+	#pragma STDC FENV_ACCESS ON
+	union ldshape u = {x};
+	int e = u.i.se & 0x7fff;
+
+	if (!e) {
+		if (x == 0) {
+			FORCE_EVAL(0/0.0f);
+			return FP_ILOGB0;
+		}
+		/* subnormal x */
+		x *= 0x1p120;
+		return ilogbl(x) - 120;
+	}
+	if (e == 0x7fff) {
+		FORCE_EVAL(0/0.0f);
+		u.i.se = 0;
+		return u.f ? FP_ILOGBNAN : INT_MAX;
+	}
+	return e - 0x3fff;
+}
+#endif