The QUnicodeTables::Properties struct contains a

    struct {
        ushort special    : 1;
        signed short diff : 15;
    } cases[NumCases];

where NumCases is 4. So this part of the struct takes 4*16 = 64 bits = 8 bytes, of a total of sizeof(Properties) == 20.

We might want to look into moving the cases into a separate table, and either just use a single bit in the Properties table to indicate that the character should be looked up (with lower_bound) in the new table, or else place an index into the new table into Properties. With the former approach, the single bit would indicate the all-zero cases struct. With the latter approach, we share the many zero entries by mapping them all to index 0 in the new table.