code: public static long crc32(byte[] bytes, int offset, int size) {
          CRC32 crc = new CRC32();
          crc.update(bytes, offset, size);
          return crc.getValue();
      }
docs: Compute the CRC32 of the segment of the byte array given by the
  specificed size and offset
  
  @param bytes  The bytes to checksum
  @param offset the offset at which to begin checksumming
  @param size   the number of bytes to checksum
  @return The CRC32