Krakout: Horizontally mirror the object sprite bank in place

BC01: Horizontally mirror the object sprite bank in place

Flips the object sprite bank left-to-right in place so every sprite faces the active play side. The mirror is its own inverse.
mirror_sprite_bank	BC01	LD HL,sprite_mirror_lut	Hold the bit-reverse table's page in the alternate bank for byte translation.
	BC04	EXX
	BC05	LD HL,slot_visor_1	Mirror the sprite bank in place, from its base.
	BC08	LD BC,$0590	Walk the whole sprite bank, two bytes at a time.
mirror_row	BC0B	LD D,(HL)	Read the row's two bytes.
	BC0C	INC HL
	BC0D	LD E,(HL)
	BC0E	DEC HL
	BC0F	PUSH DE	Pass the pair into the alternate bank for table lookup.
	BC10	EXX
	BC11	POP DE
The bit-reverse table is 256 bytes in the page at the tile-glyph base. The lowest tile codes are never written to the tile map, so those bytes are free for it. The tile glyphs begin one page higher.
	BC12	LD L,D	Mirror each byte through the bit-reverse table.
	BC13	LD D,(HL)
	BC14	LD L,E
	BC15	LD E,(HL)
	BC16	PUSH DE	Carry the mirrored bytes back into the sprite bank.
	BC17	EXX
	BC18	POP DE
	BC19	LD (HL),E	Write the mirrored bytes back in swapped order and advance to the next row.
	BC1A	INC HL
	BC1B	LD (HL),D
	BC1C	INC HL
	BC1D	DEC BC	Loop until all rows are mirrored.
	BC1E	LD A,B
	BC1F	OR C
	BC20	JR NZ,mirror_row
	BC22	RET

Routines