diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValueUtils.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValueUtils.java
index 6780035..15f8a9b 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValueUtils.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValueUtils.java
@@ -14,4 +14,16 @@
         return key ^ (value & valueMask);
     }
 
+    public static int prefixBits(long raw1, int numBits) {
+        Preconditions.checkArgument(numBits >= 0 && numBits <= 32,
+                "numBits must be in range [0, 32]");
+
+        if(numBits == 0)
+            return 0;
+
+        final int shiftDown = 64 - numBits;
+
+        return (int) (raw1 >>> shiftDown);
+    }
+
 }