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Save 9 bytes in 6502 LZSA1 depacker

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Emmanuel Marty 2019-06-08 23:52:18 +02:00 committed by GitHub
parent d564c1ecb8
commit aab82fa022
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1 changed files with 32 additions and 32 deletions
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64
asm/6502/decompress_v1.asm
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@ -44,8 +44,9 @@ DECODE_TOKEN
BNE EMBEDDED_LITERALS ; if not, count is directly embedded in token
JSR GETSRC ; get extra byte of variable literals count
CLC ; add extra byte to len from token
ADC #$07 ; (LITERALS_RUN_LEN)
; the carry is always set by the CMP above
; GETSRC doesn't change it
SBC #$F9 ; (LITERALS_RUN_LEN)
BCC PREPARE_COPY_LITERALS
BEQ LARGE_VARLEN_LITERALS ; if adding up to zero, go grab 16-bit count
@ -84,14 +85,34 @@ NO_LITERALS
JSR GETSRC ; get 8 bit offset from stream in A
STA OFFSLO ; store final match offset
CLC ; add dest + match offset
LDA PUTDST+1 ; low 8 bits
ADC OFFSLO
ADC PUTDST+1 ; low 8 bits
STA COPY_MATCH_LOOP+1 ; store back reference address
LDA #$0FF ; high 8 bits
JMP GOT_OFFSET ; go prepare match
BNE GOT_OFFSET ; go prepare match
; (*like JMP GOT_OFFSET but shorter)
SHORT_VARLEN_MATCHLEN
JSR GETSRC ; get single extended byte of variable match len
INY ; add 256 to match length
PREPARE_COPY_MATCH
TAX
PREPARE_COPY_MATCH_Y
INY
COPY_MATCH_LOOP
LDA $AAAA ; get one byte of backreference
INC COPY_MATCH_LOOP+1
BNE GETMATCH_DONE
INC COPY_MATCH_LOOP+2
GETMATCH_DONE
JSR PUTDST ; copy to destination
DEX
BNE COPY_MATCH_LOOP
DEY
BNE COPY_MATCH_LOOP
BEQ DECODE_TOKEN ; (*like JMP DECODE_TOKEN but shorter)
GET_LONG_OFFSET ; handle 16 bit offset:
JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
@ -117,8 +138,9 @@ GOT_OFFSET
BNE PREPARE_COPY_MATCH ; if not, count is directly embedded in token
JSR GETSRC ; get extra byte of variable match length
CLC
ADC #$12 ; add MATCH_RUN_LEN and MIN_MATCH_SIZE to match length
; the carry is always set by the CMP above
; GETSRC doesn't change it
SBC #$EE ; add MATCH_RUN_LEN and MIN_MATCH_SIZE to match length
BCC PREPARE_COPY_MATCH
BNE SHORT_VARLEN_MATCHLEN
@ -127,29 +149,7 @@ GOT_OFFSET
TAY ; put high 8 bits in Y
; large match length with zero high byte?
BEQ DECOMPRESSION_DONE ; if so, this is the EOD code, bail
JMP PREPARE_COPY_MATCH_Y
SHORT_VARLEN_MATCHLEN
JSR GETSRC ; get single extended byte of variable match len
INY ; add 256 to match length
PREPARE_COPY_MATCH
TAX
PREPARE_COPY_MATCH_Y
INY
COPY_MATCH_LOOP
LDA $AAAA ; get one byte of backreference
INC COPY_MATCH_LOOP+1
BNE GETMATCH_DONE
INC COPY_MATCH_LOOP+2
GETMATCH_DONE
JSR PUTDST ; copy to destination
DEX
BNE COPY_MATCH_LOOP
DEY
BNE COPY_MATCH_LOOP
JMP DECODE_TOKEN
BNE PREPARE_COPY_MATCH_Y ; (*like JMP PREPARE_COPY_MATCH_Y but shorter)
GETPUT
JSR GETSRC