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;;; see titlecompression.txt to understand how this works!
; cl65 -o comptitle.xex -t none comptitle.s
; comptitle.s.in is used by titlecomp.pl, to generate comptitle.s.
; __VARIABLE__ stuff is filled in by titlecomp.pl, q.v.
; DON'T bother to edit comptitle.s (edit the .in file instead)!
.include "atari.inc"
; size of uncompressed image, in bytes (but, needs to be
; a multiple of $100).
;imgsize = __SIZE__
imgsize = $1700
; these both need to be page-aligned. destination also needs
; to be aligned on a 4K boundary.
start = $9000
;destination = $2400
srcptr = FR0
dstptr = FR0+2
pagecount = FR0+4
tmp = FR0+5
.word $ffff
.word start
.word end-1
.org start
compdata:
.incbin "comptitle.dat"
; table runs __FIRSTCODE__ to __LASTCODE__
table:
__TABLE__
; decompression code starts here
init:
lda #0
sta SDMCTL ; turn off the screen. newtitle.s turns it back on.
;;; for benchmarking only, remove!
;sta RTCLOK
;sta RTCLOK+1
;sta RTCLOK+2
lda #>imgsize
sta pagecount
lda #>compdata
sta srcptr+1
lda #>destination
sta dstptr+1
lda #0
sta srcptr
sta dstptr
tay
copyloop:
lda (srcptr),y
bpl storebyte ; 0-127 always represent themselves
cmp #__LASTCODE__+1
bcs storebyte ; anything above the last code represents itself
sta tmp
sec
sbc #__FIRSTCODE__
bcc notcode ; anything below the 1st code represents itself
tax
lda table,x
beq notcode
; got a zero-run code. A = number of bytes of zeroes to store.
storezerorun:
sty tmp
tay
dey
lda #0
tax
szloop:
sta (dstptr,x)
jsr incdest
beq done
nohi2:
dey
bpl szloop
ldy tmp
clc
bcc storedone
notcode:
lda tmp
storebyte:
sty tmp
ldy #0
sta (dstptr),y
jsr incdest
beq done
nohi:
ldy tmp
storedone:
iny
bne copyloop
inc srcptr+1
bne copyloop ; always branch (since srcptr never wraps around to 0)
done:
;;; for benchmarking only, remove!
;.byte $02 ; CIM, drops us to atari800 monitor
rts
incdest:
inc dstptr
bne iddone
inc dstptr+1
dec pagecount
iddone:
rts
end:
.word INITAD
.word INITAD+1
.word init
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