; ; 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. ; ------------------------------------------------------------------- ; ------------------------------------------------------------------- ; 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. ; ------------------------------------------------------------------- ; ------------------------------------------------------------------- ; if literal sequences is not used (the data was crunched with the -c ; flag) then the following line can be uncommented for shorter code. ;EXOD_LITERAL_SEQUENCES_NOT_USED = 1 ; ------------------------------------------------------------------- ; zero page addresses used ; ------------------------------------------------------------------- exod_zp_len_lo = $a7 exod_zp_src_lo = $ae exod_zp_src_hi = exod_zp_src_lo + 1 exod_zp_bits_hi = $fc exod_zp_bitbuf = $fd exod_zp_dest_lo = exod_zp_bitbuf + 1 ; dest addr lo exod_zp_dest_hi = exod_zp_bitbuf + 2 ; dest addr hi exod_tabl_bi = exod_decrunch_table exod_tabl_lo = exod_decrunch_table + 52 exod_tabl_hi = exod_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) exod_decrunch: ; ------------------------------------------------------------------- ; init zeropage, x and y regs. (12 bytes) ; ldy #0 ldx #3 exod_init_zp: jsr exod_get_crunched_byte sta exod_zp_bitbuf - 1,x dex bne exod_init_zp ; ------------------------------------------------------------------- ; calculate tables (50 bytes) ; x and y must be #0 when entering ; exod_nextone: inx tya and #$0f beq exod_shortcut ; starta på ny sekvens txa ; this clears reg a lsr ; and sets the carry flag ldx exod_tabl_bi-1,y exod_rolle: rol rol exod_zp_bits_hi dex bpl exod_rolle ; c = 0 after this (rol exod_zp_bits_hi) adc exod_tabl_lo-1,y tax lda exod_zp_bits_hi adc exod_tabl_hi-1,y exod_shortcut: sta exod_tabl_hi,y txa sta exod_tabl_lo,y ldx #4 jsr exod_get_bits ; clears x-reg. sta exod_tabl_bi,y iny cpy #52 bne exod_nextone ldy #0 beq exod_begin ; ------------------------------------------------------------------- ; get bits (29 bytes) ; ; args: ; x = number of bits to get ; returns: ; a = #bits_lo ; x = #0 ; c = 0 ; z = 1 ; exod_zp_bits_hi = #bits_hi ; notes: ; y is untouched ; ------------------------------------------------------------------- exod_get_bits: lda #$00 sta exod_zp_bits_hi cpx #$01 bcc exod_bits_done exod_bits_next: lsr exod_zp_bitbuf bne exod_ok pha exod_literal_get_byte: jsr exod_get_crunched_byte bcc exod_literal_byte_gotten ror sta exod_zp_bitbuf pla exod_ok: rol rol exod_zp_bits_hi dex bne exod_bits_next exod_bits_done: rts ; ------------------------------------------------------------------- ; main copy loop (18(16) bytes) ; exod_copy_next_hi: dex dec exod_zp_dest_hi dec exod_zp_src_hi exod_copy_next: dey IFNCONST EXOD_LITERAL_SEQUENCES_NOT_USED bcc exod_literal_get_byte ENDIF lda (exod_zp_src_lo),y exod_literal_byte_gotten: sta (exod_zp_dest_lo),y exod_copy_start: tya bne exod_copy_next exod_begin: txa bne exod_copy_next_hi ; ------------------------------------------------------------------- ; decruncher entry point, needs calculated tables (21(13) bytes) ; x and y must be #0 when entering ; IFNCONST EXOD_LITERAL_SEQUENCES_NOT_USED inx jsr exod_get_bits tay bne exod_literal_start1 ELSE dey ENDIF exod_begin2: inx jsr exod_bits_next lsr iny bcc exod_begin2 IFCONST EXOD_LITERAL_SEQUENCES_NOT_USED beq exod_literal_start ENDIF cpy #$11 IFNCONST EXOD_LITERAL_SEQUENCES_NOT_USED bcc exod_sequence_start beq exod_bits_done ; ------------------------------------------------------------------- ; literal sequence handling (13(2) bytes) ; ldx #$10 jsr exod_get_bits exod_literal_start1: sta