src/main/java/org/nustaq/offheap/BinaryQueue.java
public void back( int len ) {
        if ( pollIndex >= len )
            pollIndex -= len;
        else
            pollIndex = pollIndex + capacity() - len;

    }
public void back( int len ) {
        if ( pollIndex >= len )
            pollIndex -= len;
        else
            pollIndex = pollIndex + capacity() - len;

    }
'unread' len bytes
@param len