fn q2_slots() -> [(usize, u32); 32]Expand description
Bit position of each of a 32-code chunk’s codes in the 2-bit layout:
word index (0 or 1) and the offset within it. One & 0x03030303 at
shift 2p then yields the four codes of group p, and those four are
consecutive in xe (groups 0 and 1) or xo (groups 2 and 3).