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Save 1 byte/2 cycles for small 6502 LZSA2 depacker

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Emmanuel Marty 2020-11-07 00:30:35 +01:00 committed by GitHub
parent b98f8410fe
commit 7ea6b63db8
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 3 additions and 10 deletions
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3
asm/6502/decompress_fast_v2.asm
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@ -114,7 +114,6 @@ NO_LITERALS
BNE GOT_OFFSET_LO ; go store low byte of match offset and prepare match
OFFSET_9_BIT ; 01Z: 9 bit offset
;;ASL ; shift Z (offset bit 8) in place
ROL
ROL
AND #$01
@ -134,7 +133,6 @@ REPMATCH_OR_LARGE_OFFSET
; (*same as JMP GOT_OFFSET_HI but shorter)
REPMATCH_OR_16_BIT ; rep-match or 16 bit offset
;;ASL ; XYZ=111?
BMI REP_MATCH ; reuse previous offset if so (rep-match)
; 110: handle 16 bit offset
@ -259,7 +257,6 @@ GETCOMBINEDBITS
JSR GETNIBBLE ; get nibble into bits 0-3 (for offset bits 1-4)
PLP ; merge Z bit as the carry bit (for offset bit 0)
COMBINEDBITZ
ROL ; nibble -> bits 1-4; carry(!Z bit) -> bit 0 ; carry cleared
DECOMPRESSION_DONE
RTS

10
asm/6502/decompress_small_v2.asm
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@ -109,11 +109,9 @@ NO_LITERALS
BNE GOT_OFFSET_LO ; go store low byte of match offset and prepare match
OFFSET_9_BIT ; 01Z: 9 bit offset
;;ASL ; shift Z (offset bit 8) in place
ROL
ROL
AND #$01
EOR #$FF ; set offset bits 15-9 to 1
ROL ; carry: Z bit; A: xxxxxxx1 (carry known set from BCS OFFSET_9_BIT)
ADC #$00 ; if Z bit is set, add 1 to A (bit 0 of A is now 0), otherwise bit 0 is 1
ORA #$FE ; set offset bits 15-9 to 1. reversed Z is already in bit 0
BNE GOT_OFFSET_HI ; go store high byte, read low byte of match offset and prepare match
; (*same as JMP GOT_OFFSET_HI but shorter)
@ -129,7 +127,6 @@ REPMATCH_OR_LARGE_OFFSET
; (*same as JMP GOT_OFFSET_HI but shorter)
REPMATCH_OR_16_BIT ; rep-match or 16 bit offset
;;ASL ; XYZ=111?
BMI REP_MATCH ; reuse previous offset if so (rep-match)
; 110: handle 16 bit offset
@ -242,7 +239,6 @@ GETCOMBINEDBITS
JSR GETNIBBLE ; get nibble into bits 0-3 (for offset bits 1-4)
PLP ; merge Z bit as the carry bit (for offset bit 0)
COMBINEDBITZ
ROL ; nibble -> bits 1-4; carry(!Z bit) -> bit 0 ; carry cleared
DECOMPRESSION_DONE
RTS