Difference between revisions of "Fast Degas PC1 decompressor code"
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Latest revision as of 00:52, 4 June 2018
GT Turbo posted this source a while ago on the forum. As it works beautifully and is rather fast, here is his Degas PC1 file decompressor routine in 68000 assembler:
a0 points to the PC1 file, a1 to the intended destination screen. The palette is not extracted with this code but follows the Deags standard, e.q. simply move from 2(a0) 32 bytes into the Shifter color registers.
; code by GT Turbo / Cerebral Vortex Depack_PC1: movem.l d0-d7/a0-a6,-(a7) lea 34(a0),a0 ; Debut du pic move.w #199,d4 ; 199 All_lines: move.l a1,a2 ; Destination moveq #3,d1 ; 4 Bit planes Debut_line: move.l a2,a3 moveq #0,d3 moveq #1,d5 Recup_code: moveq #0,d0 move.b (a0)+,d0 bmi.s Repete_code add.b d0,d3 addq.b #1,d3 Copy: move.b (a0)+,(a2) add.w d5,a2 eor.w #6,d5 dbra d0,Copy bra.s End_line Repete_code: neg.b d0 ; nop addq.b #1,d3 add.b d0,d3 move.b (a0)+,d2 Recopy_code: move.b d2,(a2) add.w d5,a2 eor.w #6,d5 dbra d0,Recopy_code End_line: cmp.b #40,d3 bne.s Recup_code move.l a3,a2 addq.w #2,a2 ; Plan suivant dbra d1,Debut_line lea 160(a1),a1 ; Ligne suivante dbra d4,All_lines movem.l (a7)+,d0-d7/a0-a6 rts
