243 lines
3.8 KiB
NASM
243 lines
3.8 KiB
NASM
inflate SUBROUTINE
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.inEnd EQU 2
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.offset EQU 4
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.length EQU 6
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.symbol EQU 25
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.marker1 EQU 30
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.marker2 EQU 31
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.marker3 EQU 32
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.marker4 EQU 33
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.copy EQU 34
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clc
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ldy #10
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lda (srcPointer),y
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adc srcPointer
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sta .inEnd
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dey
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lda (srcPointer),y
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adc srcPointer + 1
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sta .inEnd + 1
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clc
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lda .inEnd
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adc #16
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sta .inEnd
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lda .inEnd + 1
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adc #0
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sta .inEnd + 1
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; Get the marker symbols
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ldy #16
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lda (srcPointer),y
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sta .marker1
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iny
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lda (srcPointer),y
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sta .marker2
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iny
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lda (srcPointer),y
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sta .marker3
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iny
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lda (srcPointer),y
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sta .marker4
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; Skip header + marker symbols (16 + 4 bytes)
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clc
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lda srcPointer
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adc #20
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sta srcPointer
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lda srcPointer + 1
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adc #0
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sta srcPointer + 1
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; Main decompression loop
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ldy #0 ; Make sure that Y is zero
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.mainloop:
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lda srcPointer ; done?
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cmp .inEnd
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bne .notdone
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lda srcPointer + 1
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cmp .inEnd + 1
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bne .notdone
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rts
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.notdone:
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lda (srcPointer),y ; A = symbol
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sta .symbol
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sta $d020
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inc srcPointer
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bne .noinc1
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inc srcPointer + 1
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.noinc1:
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cmp .marker1 ; Marker1?
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beq .domarker1
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cmp .marker2 ; Marker2?
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beq .domarker2
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cmp .marker3 ; Marker3?
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beq .domarker3
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cmp .marker4 ; Marker4?
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beq .domarker4
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.literal:
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lda .symbol
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sta (dstPointer),y ; Plain copy
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inc dstPointer
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bne .mainloop
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inc dstPointer + 1
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bne .mainloop
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.domarker1:
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jmp .domarker1b
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; marker4 - "Near copy (incl. RLE)"
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.domarker4:
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lda (srcPointer),y
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inc srcPointer
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bne .noinc3
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inc srcPointer + 1
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.noinc3:
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cmp #0
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beq .literal ; Single occurance of the marker symbol (rare)
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tax
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lsr
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lsr
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lsr
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lsr
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lsr
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sta .offset
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inc .offset
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lda #0
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sta .offset + 1 ; offset = (b >> 5) + 1
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txa
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and #$1f
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tax
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lda .LZG_LENGTH_DECODE_LUT,x
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sta .length ; length = .LZG_LENGTH_DECODE_LUT[b & 0x1f]
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jmp .docopy
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; marker3 - "Short copy"
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.domarker3:
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lda (srcPointer),y
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inc srcPointer
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bne .noinc4
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inc srcPointer + 1
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.noinc4:
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cmp #0
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beq .literal ; Single occurance of the marker symbol (rare)
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tax
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lsr
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lsr
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lsr
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lsr
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lsr
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lsr
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clc
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adc #3
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sta .length ; length = (b >> 6) + 3
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txa
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and #$3f
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adc #8
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sta .offset
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lda #0
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sta .offset + 1 ; offset = (b & 0x3f) + 8
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beq .docopy
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; marker2 - "Medium copy"
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.domarker2:
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lda (srcPointer),y
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inc srcPointer
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bne .noinc5
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inc srcPointer + 1
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.noinc5:
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cmp #0
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beq .literal ; Single occurance of the marker symbol (rare)
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tax
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lsr
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lsr
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lsr
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lsr
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lsr
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sta .offset + 1
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lda (srcPointer),y
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inc srcPointer
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bne .noinc6
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inc srcPointer + 1
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.noinc6:
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clc
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adc #8
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sta .offset
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bcc .noinc7
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inc .offset + 1 ; offset = (((b & 0xe0) << 3) | b2) + 8
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.noinc7:
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txa
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and #$1f
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tax
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lda .LZG_LENGTH_DECODE_LUT,x
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sta .length ; length = .LZG_LENGTH_DECODE_LUT[b & 0x1f]
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bne .docopy
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.literal2:
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jmp .literal
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; marker1 - "Distant copy"
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.domarker1b:
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lda (srcPointer),y
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inc srcPointer
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bne .noinc8
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inc srcPointer + 1
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.noinc8:
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cmp #0
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beq .literal2 ; Single occurance of the marker symbol (rare)
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and #$1f
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tax
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lda .LZG_LENGTH_DECODE_LUT,x
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sta .length ; length = .LZG_LENGTH_DECODE_LUT[b & 0x1f]
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lda (srcPointer),y
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inc srcPointer
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bne .noinc9
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inc srcPointer + 1
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.noinc9:
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sta .offset + 1
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lda (srcPointer),y
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inc srcPointer
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bne .noinc10
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inc srcPointer + 1
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.noinc10:
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clc
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adc #$08
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sta .offset
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lda .offset + 1
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adc #$08
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sta .offset + 1 ; offset = ((b2 << 8) | (*src++)) + 2056
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; Copy corresponding data from history window
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.docopy:
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sec
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lda dstPointer
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sbc .offset
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sta .copy
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lda dstPointer + 1
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sbc .offset + 1
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sta .copy + 1
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.loop1:
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lda (.copy),y
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sta (dstPointer),y
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iny
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cpy .length
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bne .loop1
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ldy #0 ; Make sure that Y is zero
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clc
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lda dstPointer
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adc .length
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sta dstPointer
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bcc .noinc11
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inc dstPointer + 1
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.noinc11:
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jmp .mainloop
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; Lookup Table for decoding the copy length parameter
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.LZG_LENGTH_DECODE_LUT
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BYTE 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,35,48,72,128
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