code: public static int evenHash(final long value, final int mask)
      {
          int hash = (int)value ^ (int)(value >>> 32);
          hash = (hash << 1) - (hash << 8);
  
          return hash & mask;
      }
docs: Generate an even hash for a long value.
  
  @param value to be hashed.
  @param mask  mask to be applied that must be a power of 2 - 1.
  @return the hash of the value which is always even.