Nightshade: Routine at 48863

Used by the routine at GameOver.

Works out how much of the game has been completed and stores it as a percentage in PercentageHundreds (the hundreds digit) and PercentageTensAndUnits (the tens and units, as BCD).

Every bit set in the 128 bytes at VisitedCells is a cell of the village that has been visited. Every monster that has been killed counts as three more cells. The total is multiplied by 10288 and divided by 65536, so that visiting about 637 cells (or a few less when monsters have been killed) gives 100 percent.

Used by the routine at GameOver. Works out how much of the game has been completed and stores it as a percentage in PercentageHundreds (the hundreds digit) and PercentageTensAndUnits (the tens and units, as BCD). Every bit set in the 128 bytes at VisitedCells is a cell of the village that has been visited. Every monster that has been killed counts as three more cells. The total is multiplied by 10288 and divided by 65536, so that visiting about 637 cells (or a few less when monsters have been killed) gives 100 percent.
Count the visited cells.
CalculatePercentage	48863	LD HL,0	Start the count of cells at zero.
	48866	LD DE,48142	Point at the bitmap of visited cells.
	48869	LD C,128	Set the number of bytes in the bitmap to 128.
CalculatePercentage_ByteLoop	48871	LD A,(DE)	Fetch a byte of the bitmap and move on to the next.
	48872	INC DE	Fetch a byte of the bitmap and move on to the next.
	48873	LD B,8	Set a counter for the eight bits in the byte.
CalculatePercentage_BitLoop	48875	RRCA	Check the next bit of the bitmap, and move it into the carry flag.
	48876	JR NC,CalculatePercentage_NextBit
	48878	INC HL	Count the visited cell.
CalculatePercentage_NextBit	48879	DJNZ CalculatePercentage_BitLoop	Loop back until all eight bits have been counted.
	48881	DEC C	Loop back until every byte of the bitmap has been counted.
	48882	JR NZ,CalculatePercentage_ByteLoop	Loop back until every byte of the bitmap has been counted.
Add three for every monster that has been killed.
	48884	LD IY,48478	Start with the first of the four monsters.
	48888	LD B,4	Set a counter for the four monsters.
CalculatePercentage_MonsterLoop	48890	LD A,(IY+0)	Fetch the type of the monster and subtract 96.
	48893	SUB 96	Fetch the type of the monster and subtract 96.
	48895	CP 16	Jump to CalculatePercentage_NextMonster if the monster is still alive (its type is 96 to 111).
	48897	JR C,CalculatePercentage_NextMonster
	48899	LD DE,3	Add three to the count of cells.
	48902	ADD HL,DE	Add three to the count of cells.
CalculatePercentage_NextMonster	48903	LD DE,16	Set the size of a monster's entry in the object table to 16 bytes.
	48906	ADD IY,DE	Move on to the next monster.
	48908	DJNZ CalculatePercentage_MonsterLoop	Loop back until all four monsters have been counted.
Multiply the count by 10288 and divide by 65536, using BCD arithmetic for the high byte.
	48910	LD BC,10288	Set the value to add on each pass.
	48913	XOR A	Start the BCD result at zero.
	48914	EX DE,HL	Make the count of cells the number of times to add.
	48915	LD HL,0	Start the running total at zero.
CalculatePercentage_MultiplyLoop	48918	ADD HL,BC	Add the value to the total.
	48919	ADC A,0	Add any carry to the BCD result.
	48921	DAA	Adjust the BCD result.
	48922	PUSH AF	Stash the result on the stack.
	48923	DEC DE	Decrease the count.
	48924	LD A,E	Jump to CalculatePercentage_Finish if the count has reached zero.
	48925	OR D
	48926	JR Z,CalculatePercentage_Finish
	48928	POP AF	Restore the result from the stack.
	48929	JR CalculatePercentage_MultiplyLoop	Jump to CalculatePercentage_MultiplyLoop.
CalculatePercentage_Finish	48931	POP AF	Restore the result from the stack.
	48932	LD BC,144	Add 144 to the total, which rounds the percentage.
	48935	ADD HL,BC	Add any carry to the BCD result.
	48936	ADC A,0
	48938	DAA
	48939	LD (48126),A	Set the tens and units of the percentage.
	48942	LD A,0	Set the hundreds digit to one if the percentage has overflowed.
	48944	ADC A,0
	48946	LD (48125),A	Set the hundreds digit of the percentage.
	48949	RET	Return.