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;

; RLE/LZ bitmap decoder

; - support mapper

;

; Written in TASM 3.0.1

;



#define PSG_DECODER $7e84		; $4BE84 in slot 2





; Redirects calls to LoadTiles4BitRLENoDI@$0486 (decompress graphics, interrupt-unsafe version)

; to a ripped decompressor from Phantasy Star Gaiden which is stored at the above address

; Thus the remainder of the old decompressor is orphaned.



.org $0486			; $486-493 inclusive



	ld a,$12		; Remap page 1

	ld ($fffe),a



	call PSG_DECODER



	ld a,$01		; Restore page 1

	ld ($fffe),a



	ret



	.end			; TASM-only



; replaces:

;LoadTiles4BitRLENoDI:  ; $0486

;    ld b,$04

;  -:push bc

;        push de

;            call + ; called 4 times for 4 bitplanes

;        pop de

;        inc de

;    pop bc

;    djnz -

;    ret

;  +:

; --:ld a,(hl)          ; read count byte <----+

;    inc hl             ; increment pointer    |

;    or a               ; return if zero       |

;    ret z              ;                      |

;                       ;                      |

;    ld c,a             ; get low 7 bits in b  |

;    and $7f            ;                      |

;    ld b,a             ;                      |

;    ld a,c             ; set z flag if high   |

;    and $80            ; bit = 0              |

;                       ;                      |

;  -:SetVRAMAddressToDE ; <------------------+ |

;    ld a,(hl)          ; Get data byte in a | |

;    out (VDPData),a    ; Write it to VRAM   | |

;    jp z,+             ; If z flag then  -+ | |

;                       ; skip inc hl      | | |

;    inc hl             ;                  | | |

;                       ;                  | | |

;  +:inc de             ; Add 4 to de <----+ | |

;    inc de             ;                    | |

;    inc de             ;                    | |

;    inc de             ;                    | |

;    djnz -             ; repeat block  -----+ |

;                       ; b times              |

;    jp nz,--           ; If not z flag then --+

;    inc hl             ; inc hl here instead  |

;    jp --              ; repeat forever ------+

;                       ; (zero count byte quits)