diff --git a/libm/src/s_ilogbl.c b/libm/src/s_ilogbl.c
new file mode 100644
index 0000000..406ad56
--- /dev/null
+++ b/libm/src/s_ilogbl.c
@@ -0,0 +1,54 @@
+/*
+ * From: @(#)s_ilogb.c 5.1 93/09/24
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#ifndef lint
+static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_ilogbl.c,v 1.1 2004/10/11 18:13:52 stefanf Exp $";
+#endif
+
+#include <float.h>
+#include <limits.h>
+#include <math.h>
+
+#include "fpmath.h"
+
+int
+ilogbl(long double x)
+{
+	union IEEEl2bits u;
+	unsigned long m;
+	int b;
+
+	u.e = x;
+	if (u.bits.exp == 0) {
+		if ((u.bits.manl | u.bits.manh) == 0)
+			return (FP_ILOGB0);
+		/* denormalized */
+		if (u.bits.manh == 0) {
+			m = 1lu << (LDBL_MANL_SIZE - 1);
+			for (b = LDBL_MANH_SIZE; !(u.bits.manl & m); m >>= 1)
+				b++;
+		} else {
+			m = 1lu << (LDBL_MANH_SIZE - 1);
+			for (b = 0; !(u.bits.manh & m); m >>= 1)
+				b++;
+		}
+#ifdef LDBL_IMPLICIT_NBIT
+		b++;
+#endif
+		return (LDBL_MIN_EXP - b - 1);
+	} else if (u.bits.exp < (LDBL_MAX_EXP << 1) - 1)
+		return (u.bits.exp - LDBL_MAX_EXP + 1);
+	else if (u.bits.manl != 0 || u.bits.manh != 0)
+		return (FP_ILOGBNAN);
+	else
+		return (INT_MAX);
+}