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Save 1 byte/2 cycles for fast 6502 LZSA2 depacker

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Emmanuel Marty 2020-11-07 08:41:31 +01:00 committed by GitHub
parent 7ea6b63db8
commit d85fc4e034
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1 changed files with 3 additions and 4 deletions
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asm/6502/decompress_fast_v2.asm
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@ -114,10 +114,9 @@ NO_LITERALS
BNE GOT_OFFSET_LO ; go store low byte of match offset and prepare match
OFFSET_9_BIT ; 01Z: 9 bit offset
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)