dos33fsprogs/asm_routines/lzss_decompress.s
2018-02-09 00:46:20 -05:00

211 lines
3.5 KiB
ArmAsm

;; Our Zero Page Allocations
;; for the LZSS part of the code
OUTPUTL EQU $FE
OUTPUTH EQU $FF
LOGOL EQU $28
LOGOH EQU $29
STORERL EQU $95
STORERH EQU $96
COUNT EQU $97
;LZSS_MASK EQU $98
LOGOENDL EQU $99
LOGOENDH EQU $9A
LOADRL EQU $9B
LOADRH EQU $9C
EFFECTRL EQU $9D
EFFECTRH EQU $9E
;; LZSS Parameters
N EQU 1024
F EQU 64
THRESHOLD EQU 2
P_BITS EQU 10
POSITION_MASK EQU 3
FREQUENT_CHAR EQU 0
;R: .res (1024-64) ; N-F
R EQU $9800
; Init
lzss_init:
ldx #<R
stx OUTL
ldx #>R
stx OUTH
lda #FREQUENT_CHAR
ldx #$4
lzss_init_outer:
ldy #$0
lzss_init_inner:
sta (OUTL),Y
iny
bne lzss_init_inner
inc OUTH
dex
bpl lzss_init_inner
rts
;================================
; Decomress
; FIXME: optimize
;================================
lzss_decompress:
lda #>(N-F) ; load R value
sta STORERH
lda #<(N-F)
sta STORERL
ldy #0 ; setup Y for indirect zero page
; addressing, we always want +0
decompression_loop:
lda #8 ; set mask counter
sta COUNT
lda (LOGOL),Y ; load byte
sta LZSS_MASK ; store it
ldx #LOGOL
jsr inc16 ; increment pointer
test_flags:
lda LOGOH ; compare to see if we've reached end
cmp LOGOENDH
bne not_match
lda LOGOL
cmp LOGOENDL
beq done_logo ; if so, we are done
; bcs one byte less than jmp
not_match:
lsr LZSS_MASK ; shift byte mask into carry flag
lda (LOGOL),Y ; load byte
ldx #LOGOL ; 16-bit increrment
jsr inc16
bcs discrete_char ; if set we have discrete char
offset_length:
sta LOADRL ; bottom of R offset
lda (LOGOL),Y ; load another byte
ldx #LOGOL ;
jsr inc16 ; 16 bit increment
sta LOADRH ; top of R offset
lsr A
lsr A ; shift right by 10 (top byte by 2)
clc
adc #3 ; add threshold+1 (3)
tax ; store out count in X
output_loop:
clc ; calculate R+LOADR
lda LOADRL
adc #<R
sta EFFECTRL
lda LOADRH
and #((N-1)>>8) ; Mask so mod N
sta LOADRH
adc #>R
sta EFFECTRH
lda (EFFECTRL),Y ; Load byte R[LOADR]
inc LOADRL ; increment address
bne load_carry1
inc LOADRH ; handle overflow
load_carry1:
store_byte:
sta (OUTPUTL),Y ; store byte to output
inc OUTPUTL ; increment address
bne sb_carry
inc OUTPUTH ; handle overflow
sb_carry:
pha ; calculate R+STORER
clc
lda STORERL
adc #<R
sta EFFECTRL
lda STORERH
and #((N-1)>>8) ; mask so mod N
sta STORERH
adc #>R
sta EFFECTRH
pla ; restore from stack
sta (EFFECTRL),Y ; store A there too
inc STORERL ; increment address
bne store_carry2
inc STORERH ; handle overflow
store_carry2:
dex ; count down the out counter
bne output_loop ; loop to output_loop if not 0
dec COUNT ; count down the mask counter
bne test_flags ; loop to test_flags if not zero
beq decompression_loop ; restart whole process
discrete_char:
ldx #1 ; want to write a single byte
bne store_byte ; go and store it (1 byte less than jmp)
done_logo:
rts
;==================================================
; inc16 - increments a 16-bit pointer in zero page
;==================================================
inc16:
inc 0,X ; increment address
bne not_zero
inx
inc 0,X ; handle overflow
not_zero:
rts
;; *********************
;; BSS
;; *********************
;.bss
;R: .res (1024-64) ; N-F