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Improve hotpath of 6502 depacker further

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emmanuel-marty 2019-04-10 19:41:41 +02:00
parent 2451d5802e
commit 4c5d44fff4
1 changed files with 12 additions and 13 deletions
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25
asm/6502/decompress.asm
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@ -82,14 +82,13 @@ COPY_LITERALS
NO_LITERALS
PLA ; retrieve token from stack
PHA ; preserve token again
AND #$80 ; isolate match offset mode (O)
BNE GET_LONG_OFFSET ; $80: 16 bit offset
BMI GET_LONG_OFFSET ; $80: 16 bit offset
JSR GETSRC ; get 8 bit offset from stream in A
; Y (high 8 bits) is already set to 0 here
JMP FIX_OFFSET ; go increase offset
GET_LONG_OFFSET ; $00: 2-byte offset
GET_LONG_OFFSET ; handle 16 bit offset:
JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
TAY ; put high 8 bits in Y
TXA ; put low 8 bits in A
@ -113,17 +112,9 @@ OFFSET_FIXED
JSR GETSRC ; get extra byte of variable match length
CMP #$FF ; FF <low 8 bits> <high 8 bits>?
BEQ LARGE_VARLEN_MATCHLEN ; yes, go grab it
BNE SHORT_VARLEN_MATCHLEN ; if not, handle <8 bits> or <FE> <8 extra bits> sequence
JSR GETSINGLEVARLENSRC ; handle single extra byte of variable match len
CLC ; add extra byte to len from token
ADC #$0F ; (MATCH_RUN_LEN)
BCC PREPARE_COPY_MATCH
INY
JMP PREPARE_COPY_MATCH
LARGE_VARLEN_MATCHLEN ; FF <low 8 bits> <high 8 bits>
; Handle FF <low 8 bits> <high 8 bits>:
; match length = directly these 16 bits
JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
TAY ; put high 8 bits in Y
@ -131,6 +122,14 @@ LARGE_VARLEN_MATCHLEN ; FF <low 8 bits> <high 8 bits>
BEQ DECOMPRESSION_DONE ; if so, this is the EOD code, bail
JMP PREPARE_COPY_MATCH_Y
SHORT_VARLEN_MATCHLEN
JSR GETSINGLEVARLENSRC ; handle single extra byte of variable match len
CLC ; add extra byte to len from token
ADC #$0F ; (MATCH_RUN_LEN)
BCC PREPARE_COPY_MATCH
INY
PREPARE_COPY_MATCH
CLC ; add MIN_MATCH_SIZE to match length
ADC #$03