Used by the routines at HIT_BOXES_U and HIT_BOXES_V.

Takes the cell at column D and row H -- the high bytes of any U and V in it -- and returns its type from the map (TOWN), and the object's position in that cell's own frame, in the units its boxes are measured in: the object's U and V less the cell's corner, halved, plus 64. A cell is 256 units a side, so it runs from 64 to 191 in these half units, and a position half a cell beyond it either way still fits in a byte; only the low byte of the halved difference is kept, which is right for anything within that distance.

The entry point TOWN_CELL does only the look-up, for a column in L and a row in H; the finds (SPAWN_FIND), the visited cells (VISIT_CELL), the monsters (SPAWN_MONSTER) and the bonus (PLACE_BONUS) use it. The map is 32 cells a row, and nothing here checks that the column or the row is less than 32.