variable length tag descriptions (downwards compatibility)

brouter-util/src/main/java/btools/util/ByteArrayUnifier.java

@@ -0,0 +1,40 @@
+package btools.util;
+
+public final class ByteArrayUnifier
+{
+  private byte[][] byteArrayCache;
+  private int size;
+
+  public ByteArrayUnifier( int size )
+  {
+    this.size = size;
+    byteArrayCache = new byte[size][];
+  }
+
+  /**
+   * Unify a byte array in order to reuse instances when possible.
+   * The byte arrays are assumed to be treated as immutable,
+   * allowing the reuse
+   * @param the byte array to unify
+   * @return the cached instance or the input instanced if not cached
+   */
+  public byte[] unify( byte[] ab )
+  {
+	  int n = ab.length;
+      int crc  = Crc32.crc( ab, 0, n );
+      int idx  =  (crc & 0xfffffff) % size;
+      byte[] abc = byteArrayCache[idx];
+      if ( abc != null && abc.length == n )
+      {
+    	int i = 0;
+        while( i < n )
+        {
+        	if ( ab[i] != abc[i] ) break;
+        	i++;
+        }
+        if ( i == n ) return abc;
+      }
+      byteArrayCache[idx] = ab;
+	  return ab;
+  }
+}