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; text decompressor for taipan.
; text is packed 6 bits per character. see textcomp.c
; for details.
.include "atari.inc"
.export _print_msg
.import _cputc
srcptr = FR1
outbyte = FR0 ; decoded 6-bit byte
bitcount = FR0+1 ; counts 8..1, current bit in inbyte
inbyte = FR0+2
ysave = FR0+3
dict_escape = FR0+4
.code ; this really should be rodata, but bank 2 has no space (yet)
; one or two letter words are not worth listing here. 3 is only good
; if it's used pretty often.
; entry 0 is a dummy! The encoder gets confused by "Z\0". This may get fixed.
dict00:
dict01: .byte $98, $9d, $73, $54, $53, $80 ; "Li Yuen", 4 occurrences
dict02: .byte $7c, $c1, $05, $4b, $57, $12, $3d, $42, $05, $48, $00 ; "Elder Brother", 3
dict03: .byte $64, $f5, $40 ; "you", 30
dict04: .byte $d7, $c1, $4d, $00 ; " 'em", 8
dict05: .byte $cc, $f5, $40 ; "You", 16
dict06: .byte $d4, $80, $56, $14, $00 ; " have", 11
dict07: .byte $d5, $32, $01, $30, $c0, $00 ; " shall", 6
dict08: .byte $fb, $5c, $49, $50, $8d, $40 ; ") With ", 2
dict09: .byte $05, $21, $cf, $00 ; "argo", 6
dict10: .byte $4c, $82, $50, $00 ; "ship", 10
dict11: .byte $d5, $70, $52, $14, $83, $d5, $4c, $50, $00 ; " warehouse", 4
dict12: .byte $d5, $42, $05, $00 ; " the" 17
dict13: .byte $d4, $f1, $80 ; " of", 14
dict14: .byte $5c, $93, $0c, $00 ; "will", 8
dict15: .byte $d4, $21, $45, $3b, $50, $00 ; " been ", 6
dict16: .byte $d5, $43, $f5, $00 ; " to ", 12
dict17: .byte $20, $14, $f5, $00 ; "has ", 7
dict18: .byte $18, $f4, $b5, $00 ; "for ", 7
dict19: .byte $25, $3d, $40 ; "is ", 9
dict20: .byte $04, $e1, $00 ; "and", 10
dict21: .byte $d4, $30, $53, $20, $00 ; " cash", 8
dict22: .byte $04, $41, $09, $50, $93, $ce, $04, $cd, $40 ; "additional ", 3
dict23: .byte $b8, $12, $50, $04, $e0, $00 ; "Taipan", 3 (but really many more!)
dict_lo: .byte <dict00, <dict01, <dict02, <dict03, <dict04, <dict05, <dict06, <dict07, <dict08, <dict09, <dict10, <dict11, <dict12, <dict13, <dict14, <dict15, <dict16, <dict17, <dict18, <dict19, <dict20, <dict21, <dict22, <dict23
dict_hi: .byte >dict00, >dict01, >dict02, >dict03, >dict04, >dict05, >dict06, >dict07, >dict08, >dict09, >dict10, >dict11, >dict12, >dict13, >dict14, >dict15, >dict16, >dict17, >dict18, >dict19, >dict20, >dict21, >dict22, >dict23
; rough calculation of how many bytes are saved by the dictionary
; stuff: the dictionary + extra decoder stuff costs 221 bytes.
; each dictionary entry saves (length - 2) * (occurrences - 1) bytes.
; with only dict00 - dict21, we'll save around 147 bytes.
dictsize = * - dict00
.out .sprintf("dictionary is %d bytes", dictsize)
.rodata
table: ; outbyte values 53..63
.byte ' ', '!', '%', ',', '.', '?', ':', 39, 40, 41, $9b
tablesize = * - table
.ifdef CART_TARGET
.segment "HIGHCODE"
.else
.code
.endif
; extern void __fastcall__ print_msg(const char *msg);
_print_msg:
sta srcptr
stx srcptr+1
lda #0
sta dict_escape
sta outbyte
ldy #$ff ; since we increment it first thing...
ldx #6 ; counts 6..1, current bit in outbyte
@nextbyte:
iny
lda #8
sta bitcount
lda (srcptr),y
sta inbyte
@bitloop:
asl inbyte
rol outbyte
dex
beq @decode ; got 6 bits
dec bitcount
bne @bitloop
beq @nextbyte
@decode:
lda outbyte
bne @notend
rts ; 0 = end of message
@notend:
ldx dict_escape ; was last character a Z?
beq @normalchar
; dictionary lookup time. save our state on the stack
; TODO: see if this code's smaller using ZP instead of stack.
; it'll only be reentrant once, but that's enough.
tya
pha
lda inbyte
pha
lda srcptr
pha
lda srcptr+1
pha
lda bitcount
pha
; recursive call
ldx outbyte
lda dict_lo,x
pha
lda dict_hi,x
tax
pla
jsr _print_msg
; restore old state
lda #0
sta dict_escape
pla
sta bitcount
pla
sta srcptr+1
pla
sta srcptr
pla
sta inbyte
pla
tay
jmp @noprint
@normalchar:
cmp #27
bcs @notlower
adc #'a'-1 ; 1-26 are a-z
bne @printit
@notlower:
cmp #52
bne @notdict
inc dict_escape ; Z means next 6 bits are dictionary ID
bne @noprint
@notdict:
bcs @notupper
adc #38 ; 27-52 are A-Z
bne @printit
@notupper:
sbc #53 ; 53-63 are table lookups
tax
lda table,x
@printit:
sty ysave ; _cputc trashes Y
jsr _cputc
ldy ysave
@noprint:
lda #0
sta outbyte
ldx #6
dec bitcount
beq @nextbyte
bne @bitloop
decodersize = * - _print_msg
.out .sprintf("print_msg() is %d bytes", decodersize + tablesize)
.out .sprintf("total textdecomp is %d bytes", decodersize + tablesize + dictsize)
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