code: public long getLong(int index)
      {
          checkPositionIndexes(index, index + SIZE_OF_LONG, this.length);
          index += offset;
          return ((long) data[index] & 0xff) |
                  ((long) data[index + 1] & 0xff) << 8 |
                  ((long) data[index + 2] & 0xff) << 16 |
                  ((long) data[index + 3] & 0xff) << 24 |
                  ((long) data[index + 4] & 0xff) << 32 |
                  ((long) data[index + 5] & 0xff) << 40 |
                  ((long) data[index + 6] & 0xff) << 48 |
                  ((long) data[index + 7] & 0xff) << 56;
      }
docs: Gets a 64-bit long integer at the specified absolute {@code index} in
  this buffer.
  
  @throws IndexOutOfBoundsException if the specified {@code index} is less than {@code 0} or
  {@code index + 8} is greater than {@code this.capacity}