diff --git a/lib/div64.c b/lib/div64.c
index a111eb8..5b49191 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -77,26 +77,58 @@
 EXPORT_SYMBOL(div_s64_rem);
 #endif
 
-/* 64bit divisor, dividend and result. dynamic precision */
+/**
+ * div64_u64 - unsigned 64bit divide with 64bit divisor
+ * @dividend:	64bit dividend
+ * @divisor:	64bit divisor
+ *
+ * This implementation is a modified version of the algorithm proposed
+ * by the book 'Hacker's Delight'.  The original source and full proof
+ * can be found here and is available for use without restriction.
+ *
+ * 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c'
+ */
 #ifndef div64_u64
 u64 div64_u64(u64 dividend, u64 divisor)
 {
-	u32 high, d;
+	u32 high = divisor >> 32;
+	u64 quot;
 
-	high = divisor >> 32;
-	if (high) {
-		unsigned int shift = fls(high);
+	if (high == 0) {
+		quot = div_u64(dividend, divisor);
+	} else {
+		int n = 1 + fls(high);
+		quot = div_u64(dividend >> n, divisor >> n);
 
-		d = divisor >> shift;
-		dividend >>= shift;
-	} else
-		d = divisor;
+		if (quot != 0)
+			quot--;
+		if ((dividend - quot * divisor) >= divisor)
+			quot++;
+	}
 
-	return div_u64(dividend, d);
+	return quot;
 }
 EXPORT_SYMBOL(div64_u64);
 #endif
 
+/**
+ * div64_s64 - signed 64bit divide with 64bit divisor
+ * @dividend:	64bit dividend
+ * @divisor:	64bit divisor
+ */
+#ifndef div64_s64
+s64 div64_s64(s64 dividend, s64 divisor)
+{
+	s64 quot, t;
+
+	quot = div64_u64(abs64(dividend), abs64(divisor));
+	t = (dividend ^ divisor) >> 63;
+
+	return (quot ^ t) - t;
+}
+EXPORT_SYMBOL(div64_s64);
+#endif
+
 #endif /* BITS_PER_LONG == 32 */
 
 /*