code: public final BigInteger getUlong64() {
          final long long64 = getLong64();
  
          return (long64 >= 0) ? BigInteger.valueOf(long64) : BIGINT_MAX_VALUE.add(BigInteger.valueOf(1 + long64));
      }
docs: Return next 64-bit unsigned long from buffer. (little-endian)
  
  @see mysql-5.1.60/include/my_global.h - uint8korr