Atic Atac: Routine at 96C9

Used by the routine at DRAW_SUMMARY.

Counts the bits set in the room map and turns the total into a two-digit BCD figure at $5E54. It is not shown while playing -- DRAW_SUMMARY prints it on the GAME OVER screen, as the last of the three figures under the heading. Every third room seen is worth 2, and 1 is added at the end, so the value is (rooms / 3) * 2 + 1.

Measured by setting the map by hand and running it: 6, 7 and 8 rooms all give $05, 11 gives $07, 144 gives $97, and none at all gives $01.

The map holds 152 bits but the castle does not have 152 rooms. ROOM_TABLE has 151 entries, and of those the last two are black -- colour $00, so nothing they draw can be seen. That leaves 149 real rooms, 0 to 148, and (149 / 3) * 2 + 1 is exactly 99. The figure is scaled so that seeing everything reads 99 and it never has to carry into a third digit, which a single byte of BCD could not hold: setting all 152 bits by hand does overflow it, and $5E54 comes back $01, but no game can get there.

It is a percentage: DRAW_SUMMARY prints it after the font's percent sign (the "$" of PERCENT_LABEL is drawn as %), so every room seen reads 99%.

Used by the routine at DRAW_SUMMARY. Counts the bits set in the room map and turns the total into a two-digit BCD figure at $5E54. It is not shown while playing -- DRAW_SUMMARY prints it on the GAME OVER screen, as the last of the three figures under the heading. Every third room seen is worth 2, and 1 is added at the end, so the value is (rooms / 3) * 2 + 1. Measured by setting the map by hand and running it: 6, 7 and 8 rooms all give $05, 11 gives $07, 144 gives $97, and none at all gives $01. The map holds 152 bits but the castle does not have 152 rooms. ROOM_TABLE has 151 entries, and of those the last two are black -- colour $00, so nothing they draw can be seen. That leaves 149 real rooms, 0 to 148, and (149 / 3) * 2 + 1 is exactly 99. The figure is scaled so that seeing everything reads 99 and it never has to carry into a third digit, which a single byte of BCD could not hold: setting all 152 bits by hand does overflow it, and $5E54 comes back $01, but no game can get there. It is a percentage: DRAW_SUMMARY prints it after the font's percent sign (the "$" of PERCENT_LABEL is drawn as %), so every room seen reads 99%.
COUNT_ROOMS_EXPLORED	96C9	LD HL,$5E40	19 bytes, 8 bits each.
	96CC	LD BC,$0813	19 bytes, 8 bits each.
	96CF	LD D,$03
	96D1	XOR A
COUNT_ROOMS_EXPLORED_0	96D2	PUSH BC
	96D3	LD E,(HL)
	96D4	INC HL
COUNT_ROOMS_EXPLORED_1	96D5	RR E	Walk the bits of one byte.
	96D7	JR NC,COUNT_ROOMS_EXPLORED_2	Walk the bits of one byte.
	96D9	DEC D	Two per three rooms, in BCD -- hence the DAA.
	96DA	JR NZ,COUNT_ROOMS_EXPLORED_2
	96DC	LD D,$03
	96DE	ADD A,$02
	96E0	DAA	Keeps the running total in BCD so it can be printed a digit at a time.
COUNT_ROOMS_EXPLORED_2	96E1	DJNZ COUNT_ROOMS_EXPLORED_1
	96E3	POP BC
	96E4	DEC C
	96E5	JR NZ,COUNT_ROOMS_EXPLORED_0
	96E7	INC A	The finished figure, read back by the status panel.
	96E8	LD ($5E54),A	The finished figure, read back by the status panel.
	96EB	RET