Alien (BUGFIX 1.7): Routine at 39832

XOR-blits the Jones cat sprite (24 px wide × 21 rows, run-cycle frame 0-4 from the pointer table after JonesPhase) at pixel-X JonesPos on its fixed track (char rows 9-11). First XORs the ink bits of the 4×2 attribute block under the cat (mask = inverted top-left-of-screen ink, so the flash contrasts with the background).

Each sprite row's 3 bytes are sub-shifted by k = JonesPos&7 into 4 output bytes: for k < 4 the SRL/RR chain here right-shifts by k (the self-modifying JR at BlitJonesShiftCode is patched to skip 3-k groups); for k >= 4 BlitJonesShifted left-shifts by 8-k instead — same result, at most 4 shift passes either way.

The DJNZ at the end re-uses B: entered with B=2 (AnimJones) it falls into AdvanceJonesPos for the redraw pass.

XOR-blits the Jones cat sprite (24 px wide × 21 rows, run-cycle frame 0-4 from the pointer table after JonesPhase) at pixel-X JonesPos on its fixed track (char rows 9-11). First XORs the ink bits of the 4×2 attribute block under the cat (mask = inverted top-left-of-screen ink, so the flash contrasts with the background). Each sprite row's 3 bytes are sub-shifted by k = JonesPos&7 into 4 output bytes: for k < 4 the SRL/RR chain here right-shifts by k (the self-modifying JR at BlitJonesShiftCode is patched to skip 3-k groups); for k >= 4 BlitJonesShifted left-shifts by 8-k instead — same result, at most 4 shift passes either way. The DJNZ at the end re-uses B: entered with B=2 (AnimJones) it falls into AdvanceJonesPos for the redraw pass.
39832	PUSH BC	save B (iteration count)
39833	LD A,(22528)	A = attribute at top-left of screen (AttrFileOrigin)
39836	CPL
39837	AND 7	invert and mask ink colour bits
39839	LD (39873),A	patch XOR 7 opcode operand for attribute flash
39842	LD A,(39750)	A = JonesPos (pixel Y offset 0-135)
39845	RRA
39846	RRA
39847	RRA	A = JonesPos >> 3: character COLUMN 0-16
39848	AND 31
39850	LD E,A
39851	LD D,0	DE = the cat's character column
39853	LD HL,19488	HL = $4C20 (col 0, char row 9, pixel row 4): the run track
39856	ADD HL,DE	+ column = the cat sprite's top-left screen address
39857	LD (39751),HL	stash it in AlienScreenPtr
39860	LD HL,22848	HL = AttrRow10 (attribute row 10, col 0)
39863	ADD HL,DE	+ column = attr address of the cat's cells
39864	LD DE,29	row stride 29, not 28: the 2nd flash row lands one cell right (harmless original quirk)
39867	LD C,2	2 attribute rows
39869	LD B,4	4 attribute columns per row
39871	LD A,(HL)	flash one attribute cell:
39872	XOR 7	toggle ink colour (self-modifying: operand byte patched)
39874	LD (HL),A	write flashed attribute
39875	INC HL
39876	DJNZ 39871	next column
39878	ADD HL,DE	skip to next attribute row
39879	DEC C
39880	JR NZ,39869	next row
39882	LD HL,39753	HL -> JonesPhase
39885	LD E,(HL)	E = current run-cycle frame (0-4)
39886	LD D,0
39888	INC HL	HL -> the frame-pointer table that follows
39889	ADD HL,DE
39890	ADD HL,DE	HL -> table[phase] (2 bytes/entry)
39891	LD E,(HL)	DE = this frame's sprite data
39892	INC HL
39893	LD D,(HL)	(3 bytes x 21 rows per frame)
39894	LD A,(39750)	A = JonesPos
39897	AND 7	A = sub-cell X offset k (0-7)
39899	CP 4
39901	JP NC,40040	k >= 4: shift the other way (BlitJonesShifted)
39904	CPL	A = 3-k: shift groups to SKIP
39905	AND 3	(so k of the 3 SRL/RR groups run = right shift by k)
39907	LD L,A	patch offset = (3-k) * 7 bytes
39908	RLCA	(each skipped shift group is 7 bytes long)
39909	RLCA
39910	RLCA	A = shift_count * 8
39911	SUB L	A = shift_count * 7 (bytes to skip in shift chain)
39912	LD (39932),A	patch JR offset: BlitJonesShiftCode entry skips N SRL/RR pairs
39915	LD B,21	21 pixel rows per cat frame
39917	PUSH BC	save row counter
39918	EX DE,HL	HL = sprite data ptr
39919	LD B,(HL)	load the row's 3 sprite bytes
39920	INC HL	into B, C, E
39921	LD C,(HL)
39922	INC HL
39923	LD E,(HL)
39924	INC HL
39925	PUSH HL	save advanced sprite ptr
39926	LD HL,(39751)	HL = this row's screen address
39929	PUSH HL
39930	XOR A	A = 0: spill byte for bits shifted out
Self-modifying right-shift chain. The JR operand byte is patched before entry to skip 0-3 SRL/RR groups, giving a right-shift of 0-3 bits across the 3+1 sprite bytes in {B,C,E,A}. After shifting, the result is XOR-blitted to screen.
39931	JR 39931	self-modifying: JR offset patched to skip N SRL/RR groups
39933	SRL B	shift group 3 (shift 3 bits right)
39935	RR C
39937	RR E
39939	RRA
39940	SRL B	shift group 2
39942	RR C
39944	RR E
39946	RRA
39947	SRL B	shift group 1 (shift 1 bit right)
39949	RR C
39951	RR E
39953	RRA
39954	EX AF,AF'	swap: A' = carry spill byte
39955	LD A,B	XOR-blit the 4 result bytes:
39956	XOR (HL)
39957	LD (HL),A	XOR-blit byte 0 to screen
39958	INC HL
39959	LD A,C
39960	XOR (HL)
39961	LD (HL),A	XOR-blit byte 1
39962	INC HL
39963	LD A,E
39964	XOR (HL)
39965	LD (HL),A	XOR-blit byte 2
39966	INC HL
39967	EX AF,AF'	recover the spill byte
39968	XOR (HL)
39969	LD (HL),A	XOR-blit carry spill byte
39970	POP HL	back to the row-start screen address
39971	LD A,H	finished pixel row 7 of this char row?
39972	AND 7
39974	CP 7
39976	JR Z,39981	yes: char-row / third stepping
39978	INC H	no: next pixel row is one display bank up
39979	JR 39996
39981	LD A,L	last char row of this screen third?
39982	CP 224
39984	JR NC,39992	yes: hop to the next third
39986	LD BC,63776	no: -1760 = pixel-row 0 of the next char row
39989	ADD HL,BC
39990	JR 39996
39992	LD BC,32	+32 carries into H: row 0 of the next third
39995	ADD HL,BC
39996	LD (39751),HL	store the next row's screen address
39999	POP DE	DE = sprite ptr
40000	POP BC
40001	DJNZ 39917	next of the 21 rows
40003	POP BC	B = caller's iteration count
40004	DJNZ 40007	B was 2 (AnimJones): advance pos and redraw
40006	RET	B was 1: single XOR pass only