diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashFunc.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashFunc.java
new file mode 100644
index 0000000..f7648d7
--- /dev/null
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashFunc.java
@@ -0,0 +1,14 @@
+package org.projectfloodlight.openflow.types;
+
+/** A hash function that can hash a {@link PrimitiveSinkable}.
+ *
+ * @author Andreas Wundsam <andreas.wundsam@bigswitch.com>
+ * @param <H> - the hash.
+ */
+public interface HashFunc<H extends HashValue<H>> {
+    /** Hash the PrimitivateSinkable with this hash function and return the result */
+    public H hash(PrimitiveSinkable v);
+
+    /** Provide a defined null-hash */
+    public H nullHash();
+}
\ No newline at end of file
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValue.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValue.java
new file mode 100644
index 0000000..1dd55d5
--- /dev/null
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValue.java
@@ -0,0 +1,54 @@
+package org.projectfloodlight.openflow.types;
+
+import javax.annotation.concurrent.Immutable;
+
+/** a hash value that supports bit-wise combinations, mainly to calculate hash values for
+ *  reconciliation operations.
+ *
+ * @author Andreas Wundsam <andreas.wundsam@bigswitch.com>
+ *
+ * @param <H> - this type, for return type safety.
+ */
+@Immutable
+public interface HashValue<H extends HashValue<H>> {
+    /** return the "numBits" highest-order bits of the hash.
+     *  @param numBits number of higest-order bits to return [0-32].
+     *  @return a numberic value of the 0-32 highest-order bits.
+     */
+    int prefixBits(int numBits);
+
+    /** @return the bitwise inverse of this value */
+    H inverse();
+
+    /** or this value with another value value of the same type */
+    H or(H other);
+
+    /** and this value with another value value of the same type */
+    H and(H other);
+
+    /** xor this value with another value value of the same type */
+    H xor(H other);
+
+    /** calculate a combined hash value of this hash value (the <b>Key</b>) and the hash value
+     *  specified as a parameter (the <b>Value</b>).
+     *  <p>
+     *  The value is constructed as follows:
+     *  <ul>
+     *   <li>the first keyBits bits are taken only from the Key
+     *   <li>the other bits are taken from key xor value.
+     *  </ul>
+     *  The overall result looks like this:
+     *  <pre>
+     *  MSB                      LSB
+     *   +---------+--------------+
+     *   | key     | key ^ value  |
+     *   +---------+--------------+
+     *   |-keyBits-|
+     *  </pre>
+     *
+     * @param value - hash value to be compared with this value (the key)
+     * @param keyBits number of prefix bits that are just taken from key
+     * @return the combined value.
+     */
+    H combineWithValue(H value, int keyBits);
+}
\ No newline at end of file
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
new file mode 100644
index 0000000..6780035
--- /dev/null
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/HashValueUtils.java
@@ -0,0 +1,17 @@
+package org.projectfloodlight.openflow.types;
+
+import com.google.common.base.Preconditions;
+
+public class HashValueUtils {
+    private HashValueUtils() { }
+
+    public static long combineWithValue(long key, long value, int keyBits) {
+        Preconditions.checkArgument(keyBits >= 0 && keyBits <= 64, "keyBits must be [0,64]");
+
+        int valueBits = 64 - keyBits;
+        long valueMask = valueBits == 64 ? 0xFFFFFFFFFFFFFFFFL : (1L << valueBits) - 1;
+
+        return key ^ (value & valueMask);
+    }
+
+}