Fix a series of undefined behaviours

Fix a series of undefined behaviours

Avoid shifting negative signed integers and use typed
enum to avoids decrementing a variable beyond its defined
range, like:
       for (Rank r = RANK_8; r >= RANK_1; --r)

Changes were tested individually and passed SPRT[-3, 1].

With this patch gcc --sanitize builds cleanly.

No functional change.