Understanding concatStorage function

[glinda93]

@GNSPS First of all, thanks for writing a great library!

I'm having a hard time understanding the following line:

 switch add(lt(slength, 32), lt(newlength, 32))
            case 2 {
                // Since the new array still fits in the slot, we just need to
                // update the contents of the slot.
                // uint256(bytes_storage) = uint256(bytes_storage) + uint256(bytes_memory) + new_length

What happens when slength and newlength are lower than 31 but slength + newlength exceeds the 31 length limit?

_preBytes is now a long array and we should use a different encoding.

But as far as I understand, current implementation still regards it as a short array.

Do I miss anything?