mirror of https://github.com/fadden/fhpack.git
143 lines
3.2 KiB
ArmAsm
143 lines
3.2 KiB
ArmAsm
*********************************
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* *
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* LZ4FH uncompression for 65816 *
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* By Andy McFadden *
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* Version 1.0.1, August 2015 *
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* *
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* Refactored for size & speed *
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* by Peter Ferrie. *
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* *
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* Developed with Merlin-16 *
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* *
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*********************************
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lst off
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org $0300
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xc ;allow 65c02 opcodes
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xc ;allow 65816 opcodes
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*
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* Constants
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*
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lz4fh_magic equ $66 ;ascii 'f'
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tok_empty equ 253
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tok_eod equ 254
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*
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* Variable storage
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*
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savmix equ $00 ;2b
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savlen equ $02 ;2b
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*
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* ROM routines
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*
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bell equ $ff3a
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monitor equ $ff69
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*
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* Parameters.
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*
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* in_dst must be $2000 or $4000
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*
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in_src equ $2fc ;2b
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in_dst equ $2fe ;2b
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* Main entry point.
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entry
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clc ;go native
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xce
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rep #$30 ;16-bit acc/index
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mx %00 ; tell Merlin
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ldx in_src
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ldy in_dst
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sty _dstmod+1
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lda $0000,x
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inx
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and #$00ff
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cmp #lz4fh_magic
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beq mainloop
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fail
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jsr bell
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jmp monitor
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notempty
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cmp #tok_eod ;end-of-data or error
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* exit
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sec ;return to emulation mode
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xce
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bne fail
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rts
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mx %00 ;undo the sec/xce
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* handle "special" match length values (in A)
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specialmatch
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cmp #tok_empty
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bne notempty
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mainloop
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lda $0000,x
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inx
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sta savmix
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and #$00f0
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beq noliteral
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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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cmp #$000f
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bne shortlit
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lda $0000,x ;length >= 15, get next
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inx
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and #$00ff
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adc #14 ;(carry set) +15 - won't exceed 255
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* At this point, Y holds the address of the next
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* compressed data byte, X has the address of the
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* next output position, and A has the length of
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* the literal.
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*
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* The MVN instruction moves (A+1) bytes from X
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* to Y, advancing X and Y.
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shortlit
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dec A ;MVN wants length-1
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mvn $00,$00 ;7 cycles/byte
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* Now handle the match.
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noliteral
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lda savmix
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and #$000f
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cmp #$000f
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blt :shortmatch ;BCC
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lda $0000,x ;add length extension
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inx
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and #$00ff
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cmp #237 ;"normal" values are 0-236
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bge specialmatch
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adc #15 ;carry clear; won't exceed 255
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:shortmatch
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adc #3 ;min match, -1 for MVN
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sta savlen ;spill A while we get offset
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lda $0000,x ;load source buffer offset
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inx
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inx
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phx ;save srcptr for later
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_dstmod ora #$ff00 ;OR in hi-res page
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tax
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lda savlen
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mvn $00,$00
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plx ;restore srcptr
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bra mainloop
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lst on
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sav LZ4FH65816
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lst off
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