diff --git a/libm/src/s_logb.c b/libm/src/s_logb.c
new file mode 100644
index 0000000..30edb87
--- /dev/null
+++ b/libm/src/s_logb.c
@@ -0,0 +1,44 @@
+/* @(#)s_logb.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_logb.c,v 1.10 2005/12/03 11:57:19 bde Exp $";
+#endif
+
+/*
+ * double logb(x)
+ * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
+ * Use ilogb instead.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+static const double
+two54 = 1.80143985094819840000e+16;	/* 43500000 00000000 */
+
+double
+logb(double x)
+{
+	int32_t lx,ix;
+	EXTRACT_WORDS(ix,lx,x);
+	ix &= 0x7fffffff;			/* high |x| */
+	if((ix|lx)==0) return -1.0/fabs(x);
+	if(ix>=0x7ff00000) return x*x;
+	if(ix<0x00100000) {
+		x *= two54;		 /* convert subnormal x to normal */
+		GET_FLOAT_WORD(ix,x);
+		ix &= 0x7fffffff;
+		return (float) ((ix>>20)-1023-54);
+	} else
+		return (double) ((ix>>20)-1023);
+}