From c220694531a25a6b80d42214a5870bd50874eaca Mon Sep 17 00:00:00 2001 From: emmanuel-marty Date: Wed, 10 Apr 2019 17:30:24 +0200 Subject: [PATCH] Add 6502 decompressor --- asm/6502/decompress.asm | 207 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 207 insertions(+) create mode 100755 asm/6502/decompress.asm diff --git a/asm/6502/decompress.asm b/asm/6502/decompress.asm new file mode 100755 index 0000000..f531a3b --- /dev/null +++ b/asm/6502/decompress.asm @@ -0,0 +1,207 @@ +; ----------------------------------------------------------------------------- +; Decompress raw LZSA block. Create one with lzsa -r +; +; in: +; * LZSA_SRC_LO and LZSA_SRC_HI contain the compressed raw block address +; * LZSA_DST_LO and LZSA_DST_HI contain the destination buffer address +; +; out: +; * LZSA_DST_LO and LZSA_DST_HI contain the last decompressed byte address, +1 +; ----------------------------------------------------------------------------- +; +; Copyright (C) 2019 Emmanuel Marty +; +; 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 source distribution. +; ----------------------------------------------------------------------------- + +OFFSLO = $43 ; zero-page location for temp offset +OFFSHI = $44 + +DECOMPRESS_LZSA + LDY #$00 + +DECODE_TOKEN + JSR GETSRC ; read token byte: O|LLL|MMMM + PHA ; preserve token on stack + + AND #$70 ; isolate literals count + BEQ NO_LITERALS ; skip if no literals to copy + CMP #$70 ; LITERALS_RUN_LEN? + BNE EMBEDDED_LITERALS ; if not, count is directly embedded in token + + JSR GETSRC ; get extra byte of variable literals count + CMP #$FF ; FF ? + BEQ LARGE_VARLEN_LITERALS ; yes, go grab it + + JSR GETSINGLEVARLENSRC ; handle single extra byte of variable literals count + + CLC ; add extra byte to len from token + ADC #$07 ; (LITERALS_RUN_LEN) + BCC PREPARE_COPY_LITERALS + INY + JMP PREPARE_COPY_LITERALS + +LARGE_VARLEN_LITERALS ; FF + ; literals count = directly these 16 bits + JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A + TAY ; put high 8 bits in Y + JMP PREPARE_COPY_LITERALS_HIGH + +EMBEDDED_LITERALS + LSR A ; shift literals count into place + LSR A + LSR A + LSR A + +PREPARE_COPY_LITERALS + TAX +PREPARE_COPY_LITERALS_HIGH + INY + +COPY_LITERALS + JSR GETPUT ; copy one byte of literals + DEX + BNE COPY_LITERALS + DEY + BNE COPY_LITERALS + +NO_LITERALS + PLA ; retrieve token from stack + PHA ; preserve token again + AND #$80 ; isolate match offset mode (O) + BNE GET_LONG_OFFSET ; $80: 16 bit offset + + JSR GETSRC ; get 8 bit offset from stream + TAX ; store as low 8 bits of offset + ; Y (high 8 bits) is already set to 0 here + JMP FIX_OFFSET ; go increase offset + +GET_LONG_OFFSET ; $00: 2-byte offset + JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A + TAY ; put high 8 bits in Y + +FIX_OFFSET + TXA ; add 1 to offset + CLC + ADC #$01 + BCC OFFSET_FIXED + + INY + +OFFSET_FIXED + STA OFFSLO ; store final match offset + STY OFFSHI + LDY #$00 ; reset Y again + + PLA ; retrieve token from stack again + AND #$0F ; isolate match len (MMMM) + CMP #$0F ; MATCH_RUN_LEN? + BNE PREPARE_COPY_MATCH ; if not, count is directly embedded in token + + JSR GETSRC ; get extra byte of variable match length + CMP #$FF ; FF ? + BEQ LARGE_VARLEN_MATCHLEN ; yes, go grab it + + JSR GETSINGLEVARLENSRC ; handle single extra byte of variable match len + + CLC ; add extra byte to len from token + ADC #$0F ; (MATCH_RUN_LEN) + BCC PREPARE_COPY_MATCH + INY + JMP PREPARE_COPY_MATCH + +LARGE_VARLEN_MATCHLEN ; FF + ; match length = directly these 16 bits + JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A + TAY ; put high 8 bits in Y + ; large match length with zero high byte? + BEQ DECOMPRESSION_DONE ; if so, this is the EOD code, bail + JMP PREPARE_COPY_MATCH_Y + +PREPARE_COPY_MATCH + CLC ; add MIN_MATCH_SIZE to match length + ADC #$03 + BCC MIN_MATCH_SIZE_ADDED + INY + +MIN_MATCH_SIZE_ADDED + TAX +PREPARE_COPY_MATCH_Y + INY + +COPY_MATCH + SEC ; substract dest - match offset + LDA PUTDST+1 ; low 8 bits + SBC OFFSLO + STA COPY_MATCH_LOOP+1 ; store back reference address + LDA PUTDST+2 ; high 8 bits + SBC OFFSHI + STA COPY_MATCH_LOOP+2 ; store high 8 bits of address + +COPY_MATCH_LOOP + LDA $AAAA ; get one byte of backreference + INC COPY_MATCH_LOOP+1 + BNE GETMATCH_DONE + INC COPY_MATCH_LOOP+2 +GETMATCH_DONE + JSR PUTDST ; copy to destination + DEX + BNE COPY_MATCH_LOOP + DEY + BNE COPY_MATCH_LOOP + JMP DECODE_TOKEN + +GETPUT + JSR GETSRC +PUTDST +LZSA_DST_LO = *+1 +LZSA_DST_HI = *+2 + STA $AAAA + INC PUTDST+1 + BNE PUTDST_DONE + INC PUTDST+2 +PUTDST_DONE +DECOMPRESSION_DONE + RTS + +GETLARGESRC + JSR GETSRC ; grab low 8 bits + TAX ; move to X + ; fall through grab high 8 bits + +GETSRC +LZSA_SRC_LO = *+1 +LZSA_SRC_HI = *+2 + LDA $AAAA + INC GETSRC+1 + BNE GETSRC_DONE + INC GETSRC+2 +GETSRC_DONE + RTS + +GETSINGLEVARLENSRC + CMP #$FE ; FE ? + BNE SINGLE_VARLEN_ADDED ; no, just this byte + + JSR GETSRC ; get extra byte of variable literals count + CLC ; add $FE to len from token + ADC #$FE + BCC SINGLE_VARLEN_ADDED + INY + +SINGLE_VARLEN_ADDED + RTS