This is not necessarily true, as we discussed. Take for example sz=2^10+2^9 and P_SZ=2^8, so doing
(2^10 + 2^9) AND (2^8-1) results in 0.

If we could assume both sizes are powers of 2, we would just directly compare sz >= SZ to know if SZ is a divisor.

In any case the suggested change is a bug.