; ; Copyright (c) 2002 - 2005 Magnus Lind. ; ; This software is provided 'as-is', without any express or implied warranty. ; In no event will the authors be held liable for any damages arising from ; the use of this software. ; ; Permission is granted to anyone to use this software for any purpose, ; including commercial applications, and to alter it and redistribute it ; freely, subject to the following restrictions: ; ; 1. The origin of this software must not be misrepresented; you must not ; claim that you wrote the original software. If you use this software in a ; product, an acknowledgment in the product documentation would be ; appreciated but is not required. ; ; 2. Altered source versions must be plainly marked as such, and must not ; be misrepresented as being the original software. ; ; 3. This notice may not be removed or altered from any distribution. ; ; 4. The names of this software and/or it's copyright holders may not be ; used to endorse or promote products derived from this software without ; specific prior written permission. ; ; ------------------------------------------------------------------- ; The decruncher jsr:s to the get_crunched_byte address when it wants to ; read a crunched byte. This subroutine has to preserve x and y register ; and must not modify the state of the carry flag. ; ------------------------------------------------------------------- .import get_crunched_byte ; ------------------------------------------------------------------- ; this function is the heart of the decruncher. ; It initializes the decruncher zeropage locations and precalculates the ; decrunch tables and decrunches the data ; This function will not change the interrupt status bit and it will not ; modify the memory configuration. ; ------------------------------------------------------------------- .export decrunch ; ------------------------------------------------------------------- ; if literal sequences is not used (the data was crunched with the -c ; flag) then the following line can be uncommented for shorter code. ;LITERAL_SEQUENCES_NOT_USED = 1 ; ------------------------------------------------------------------- ; zero page addresses used ; ------------------------------------------------------------------- zp_len_lo = $a7 zp_src_lo = $ae zp_src_hi = zp_src_lo + 1 zp_bits_hi = $fc zp_bitbuf = $fd zp_dest_lo = zp_bitbuf + 1 ; dest addr lo zp_dest_hi = zp_bitbuf + 2 ; dest addr hi tabl_bi = decrunch_table tabl_lo = decrunch_table + 52 tabl_hi = decrunch_table + 104 ; ------------------------------------------------------------------- ; no code below this comment has to be modified in order to generate ; a working decruncher of this source file. ; However, you may want to relocate the tables last in the file to a ; more suitable address. ; ------------------------------------------------------------------- ; ------------------------------------------------------------------- ; jsr this label to decrunch, it will in turn init the tables and ; call the decruncher ; no constraints on register content, however the ; decimal flag has to be #0 (it almost always is, otherwise do a cld) decrunch: ; ------------------------------------------------------------------- ; init zeropage, x and y regs. (12 bytes) ; ldy #0 ldx #3 init_zp: jsr get_crunched_byte sta zp_bitbuf - 1,x dex bne init_zp ; ------------------------------------------------------------------- ; calculate tables (50 bytes) ; x and y must be #0 when entering ; nextone: inx tya and #$0f beq shortcut ; starta på ny sekvens txa ; this clears reg a lsr a ; and sets the carry flag ldx tabl_bi-1,y rolle: rol a rol zp_bits_hi dex bpl rolle ; c = 0 after this (rol zp_bits_hi) adc tabl_lo-1,y tax lda zp_bits_hi adc tabl_hi-1,y shortcut: sta tabl_hi,y txa sta tabl_lo,y ldx #4 jsr get_bits ; clears x-reg. sta tabl_bi,y iny cpy #52 bne nextone ldy #0 beq begin ; ------------------------------------------------------------------- ; get bits (29 bytes) ; ; args: ; x = number of bits to get ; returns: ; a = #bits_lo ; x = #0 ; c = 0 ; z = 1 ; zp_bits_hi = #bits_hi ; notes: ; y is untouched ; ------------------------------------------------------------------- get_bits: lda #$00 sta zp_bits_hi cpx #$01 bcc bits_done bits_next: lsr zp_bitbuf bne ok pha literal_get_byte: jsr get_crunched_byte bcc literal_byte_gotten ror a sta zp_bitbuf pla ok: rol a rol zp_bits_hi dex bne bits_next bits_done: rts ; ------------------------------------------------------------------- ; main copy loop (18(16) bytes) ; copy_next_hi: dex dec zp_dest_hi dec zp_src_hi copy_next: dey .IFNDEF LITERAL_SEQUENCES_NOT_USED bcc literal_get_byte .ENDIF lda (zp_src_lo),y literal_byte_gotten: sta (zp_dest_lo),y copy_start: tya bne copy_next begin: txa bne copy_next_hi ; ------------------------------------------------------------------- ; decruncher entry point, needs calculated tables (21(13) bytes) ; x and y must be #0 when entering ; .IFNDEF LITERAL_SEQUENCES_NOT_USED inx jsr get_bits tay bne literal_start1 .ELSE dey .ENDIF begin2: inx jsr bits_next lsr a iny bcc begin2 .IFDEF LITERAL_SEQUENCES_NOT_USED beq literal_start .ENDIF cpy #$11 .IFNDEF LITERAL_SEQUENCES_NOT_USED bcc sequence_start beq bits_done ; ------------------------------------------------------------------- ; literal sequence handling (13(2) bytes) ; ldx #$10 jsr get_bits literal_start1: sta