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Peter Ferrie
parent
36e7316f30
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@ -29,15 +29,10 @@
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; 3. This notice may not be removed or altered from any source distribution.
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; -----------------------------------------------------------------------------
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OFFSLO = $43 ; zero-page location for temp offset
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OFFSHI = $44
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FIXUP = $4B
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NIBBLES = $FB
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NIBCOUNT = $FC
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NIBCOUNT = $FC ; zero-page location for temp offset
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DECOMPRESS_LZSA2
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LDY #$00
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STY NIBBLES
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STY NIBCOUNT
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DECODE_TOKEN
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@ -51,7 +46,7 @@ DECODE_TOKEN
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JSR GETNIBBLE ; get extra literals length nibble
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; add nibble to len from token
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ADC #$03 ; (LITERALS_RUN_LEN_V2)
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ADC #$02 ; (LITERALS_RUN_LEN_V2) minus carry
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CMP #$12 ; LITERALS_RUN_LEN_V2 + 15 ?
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BNE PREPARE_COPY_LITERALS ; if less, literals count is complete
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@ -87,22 +82,22 @@ COPY_LITERALS
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NO_LITERALS
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PLA ; retrieve token from stack
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PHA ; preserve token again
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BMI REPMATCH_OR_LARGE_OFFSET ; 1YZ: rep-match or 13/16 bit offset
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ASL
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BCS REPMATCH_OR_LARGE_OFFSET ; 1YZ: rep-match or 13/16 bit offset
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ASL ; 0YZ: 5 or 9 bit offset
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BMI OFFSET_9_BIT
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BCS OFFSET_9_BIT
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; 00Z: 5 bit offset
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LDX #$0FF ; set offset bits 15-8 to 1
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STX OFFSHI
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JSR GETCOMBINEDBITS ; rotate Z bit into bit 0, read nibble for bits 4-1
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ORA #$E0 ; set bits 7-5 to 1
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BNE GOT_OFFSET_LO ; go store low byte of match offset and prepare match
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OFFSET_9_BIT ; 01Z: 9 bit offset
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ASL ; shift Z (offset bit 8) in place
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;;ASL ; shift Z (offset bit 8) in place
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ROL
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ROL
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AND #$01
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@ -112,7 +107,7 @@ OFFSET_9_BIT ; 01Z: 9 bit offset
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REPMATCH_OR_LARGE_OFFSET
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ASL ; 13 bit offset?
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BMI REPMATCH_OR_16_BIT ; handle rep-match or 16-bit offset if not
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BCS REPMATCH_OR_16_BIT ; handle rep-match or 16-bit offset if not
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; 10Z: 13 bit offset
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@ -122,36 +117,38 @@ REPMATCH_OR_LARGE_OFFSET
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; (*same as JMP GOT_OFFSET_HI but shorter)
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REPMATCH_OR_16_BIT ; rep-match or 16 bit offset
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ASL ; XYZ=111?
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;;ASL ; XYZ=111?
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BMI REP_MATCH ; reuse previous offset if so (rep-match)
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; 110: handle 16 bit offset
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JSR GETSRC ; grab high 8 bits
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GOT_OFFSET_HI
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STA OFFSHI ; store high byte of match offset
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TAX
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JSR GETSRC ; grab low 8 bits
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GOT_OFFSET_LO
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STA OFFSLO ; store low byte of match offset
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STX OFFSHI ; store high byte of match offset
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REP_MATCH
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CLC ; add dest + match offset
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LDA PUTDST+1 ; low 8 bits
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ADC OFFSLO
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OFFSLO = *+1
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ADC #$AA
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STA COPY_MATCH_LOOP+1 ; store back reference address
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LDA OFFSHI ; high 8 bits
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OFFSHI = *+1
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LDA #$AA ; high 8 bits
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ADC PUTDST+2
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STA COPY_MATCH_LOOP+2 ; store high 8 bits of address
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PLA ; retrieve token from stack again
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AND #$07 ; isolate match len (MMM)
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CLC
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ADC #$02 ; add MIN_MATCH_SIZE_V2
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ADC #$01 ; add MIN_MATCH_SIZE_V2 and carry
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CMP #$09 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
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BNE PREPARE_COPY_MATCH ; if less, length is directly embedded in token
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JSR GETNIBBLE ; get extra match length nibble
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; add nibble to len from token
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ADC #$09 ; (MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2)
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ADC #$08 ; (MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2) minus carry
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CMP #$18 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
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BNE PREPARE_COPY_MATCH ; if less, match length is complete
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@ -165,7 +162,7 @@ REP_MATCH
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; Handle 16 bits match length
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JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
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TAY ; put high 8 bits in Y
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TXA
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.DB $A9 ; mask TAX, faster than TXA/TAX
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PREPARE_COPY_MATCH
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TAX
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@ -188,34 +185,33 @@ GETMATCH_INC_HI
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BNE GETMATCH_DONE ; (*like JMP GETMATCH_DONE but shorter)
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GETCOMBINEDBITS
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STA FIXUP
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EOR #$80
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ASL
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PHP
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JSR GETNIBBLE ; get nibble into bits 0-3 (for offset bits 1-4)
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BIT FIXUP ; merge Z bit as the carry bit (for offset bit 0)
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BVS COMBINEDBITZ
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SEC
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PLP ; merge Z bit as the carry bit (for offset bit 0)
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COMBINEDBITZ
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ROL ; nibble -> bits 1-4; carry(!Z bit) -> bit 0 ; carry cleared
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RTS
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GETNIBBLE
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NIBBLES = *+1
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LDA #$AA
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LSR NIBCOUNT
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BCS HAS_NIBBLES
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INC NIBCOUNT
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JSR GETSRC ; get 2 nibbles
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STA NIBBLES
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LSR A
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LSR A
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LSR A
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LSR A
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CLC
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RTS
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LSR
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LSR
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LSR
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LSR
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SEC
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HAS_NIBBLES
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LDA NIBBLES
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AND #$0F ; isolate low 4 bits of nibble
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CLC
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RTS
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GETPUT
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