638 lines
20 KiB
ArmAsm
638 lines
20 KiB
ArmAsm
; ***************************************************************************
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; ***************************************************************************
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;
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; lzsa2_6502.s
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;
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; NMOS 6502 decompressor for data stored in Emmanuel Marty's LZSA2 format.
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;
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; This code is written for the ACME assembler.
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;
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; Optional code is presented for two minor 6502 optimizations that break
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; compatibility with the current LZSA2 format standard.
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;
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; The code is 241 bytes for the small version, and 267 bytes for the normal.
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;
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; Copyright John Brandwood 2019.
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;
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; Distributed under the Boost Software License, Version 1.0.
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; (See accompanying file LICENSE_1_0.txt or copy at
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; http://www.boost.org/LICENSE_1_0.txt)
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;
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; ***************************************************************************
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; ***************************************************************************
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; ***************************************************************************
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; ***************************************************************************
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;
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; Decompression Options & Macros
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;
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;
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; Save 7 bytes of code, and 21 cycles every time that a
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; 16-bit length is decoded?
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;
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; N.B. Setting this breaks compatibility with LZSA v1.2
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;
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LZSA_SWAP_LEN16 = 0
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;
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; Save 3 bytes of code, and 4 or 8 cycles when decoding
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; an offset?
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;
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; N.B. Setting this breaks compatibility with LZSA v1.2
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;
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LZSA_SWAP_XZY = 0
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;
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; Choose size over space (within sane limits)?
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;
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LZSA_SMALL_SIZE = 0
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;
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; Remove code inlining to save space?
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;
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; This saves 15 bytes of code at the cost of 7% speed.
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;
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!if LZSA_SMALL_SIZE {
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LZSA_NO_INLINE = 1
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} else {
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LZSA_NO_INLINE = 0
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}
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;
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; Use smaller code for copying literals?
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;
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; This saves 11 bytes of code at the cost of 5% speed.
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;
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!if LZSA_SMALL_SIZE {
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LZSA_SHORT_CP = 1
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} else {
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LZSA_SHORT_CP = 0
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}
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;
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; Assume that we're decompressing from a large multi-bank
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; compressed data file, and that the next bank may need to
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; paged in when a page-boundary is crossed.
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;
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LZSA_FROM_BANK = 0
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;
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; We will read from or write to $FFFF. This prevents the
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; use of the "INC ptrhi / BNE" trick and reduces speed.
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;
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LZSA_USE_FFFF = 0
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;
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; Macro to increment the source pointer to the next page.
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;
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!if LZSA_FROM_BANK {
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!macro LZSA_INC_PAGE {
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jsr lzsa2_next_page
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}
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} else {
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!macro LZSA_INC_PAGE {
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inc <lzsa_srcptr + 1
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}
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}
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;
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; Macro to read a byte from the compressed source data.
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;
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!if LZSA_NO_INLINE {
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!macro LZSA_GET_SRC {
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jsr lzsa2_get_byte
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}
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} else {
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!macro LZSA_GET_SRC {
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lda (lzsa_srcptr),y
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inc <lzsa_srcptr + 0
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bne .skip
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+LZSA_INC_PAGE
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.skip:
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}
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}
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;
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; Macro to speed up reading 50% of nibbles.
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;
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; This seems to save very few cycles compared to the
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; increase in code size, and it isn't recommended.
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;
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LZSA_SLOW_NIBL = 1
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!if (LZSA_SLOW_NIBL + LZSA_SMALL_SIZE) {
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!macro LZSA_GET_NIBL {
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jsr lzsa2_get_nibble ; Always call a function.
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}
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} else {
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!macro LZSA_GET_NIBL {
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lsr <lzsa_nibflg ; Is there a nibble waiting?
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lda <lzsa_nibble ; Extract the lo-nibble.
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bcs .skip
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jsr lzsa2_new_nibble ; Extract the hi-nibble.
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.skip: ora #$F0
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}
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}
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; ***************************************************************************
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; ***************************************************************************
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;
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; Data usage is last 11 bytes of zero-page.
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;
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lzsa_cmdbuf = $F5 ; 1 byte.
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lzsa_nibflg = $F6 ; 1 byte.
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lzsa_nibble = $F7 ; 1 byte.
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lzsa_offset = $F8 ; 1 word.
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lzsa_winptr = $FA ; 1 word.
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lzsa_srcptr = $FC ; 1 word.
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lzsa_dstptr = $FE ; 1 word.
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lzsa_length = lzsa_winptr ; 1 word.
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LZSA_SRC_LO = $FC
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LZSA_SRC_HI = $FD
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LZSA_DST_LO = $FE
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LZSA_DST_HI = $FF
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; ***************************************************************************
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; ***************************************************************************
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;
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; lzsa2_unpack - Decompress data stored in Emmanuel Marty's LZSA2 format.
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;
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; Args: lzsa_srcptr = ptr to compessed data
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; Args: lzsa_dstptr = ptr to output buffer
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; Uses: lots!
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;
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; If compiled with LZSA_FROM_BANK, then lzsa_srcptr should be within the bank
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; window range.
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;
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DECOMPRESS_LZSA2_FAST:
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lzsa2_unpack: ldy #0 ; Initialize source index.
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sty <lzsa_nibflg ; Initialize nibble buffer.
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!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) = 0 {
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beq .cp_length ; always taken
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.incsrc1:
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inc <lzsa_srcptr + 1
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bne .resume_src1 ; always taken
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!if LZSA_SHORT_CP {
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.incsrc2:
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inc <lzsa_srcptr + 1
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bne .resume_src2 ; always taken
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.incdst:
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inc <lzsa_dstptr + 1
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bne .resume_dst ; always taken
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}
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}
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;
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; Copy bytes from compressed source data.
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;
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.cp_length: ldx #$00 ; Hi-byte of length or offset.
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!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) {
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+LZSA_GET_SRC
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} else {
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lda (lzsa_srcptr),y
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inc <lzsa_srcptr + 0
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beq .incsrc1
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}
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.resume_src1:
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sta <lzsa_cmdbuf ; Preserve this for later.
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and #$18 ; Extract literal length.
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beq .lz_offset ; Skip directly to match?
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lsr ; Get 2-bit literal length.
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lsr
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lsr
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cmp #$03 ; Extended length?
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bne .got_cp_len
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jsr .get_length ; X=0 table index for literals.
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!if LZSA_SHORT_CP {
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.got_cp_len: cmp #0 ; Check the lo-byte of length.
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beq .put_cp_len
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inx ; Increment # of pages to copy.
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.put_cp_len: stx <lzsa_length
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tax
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.cp_page: lda (lzsa_srcptr),y
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sta (lzsa_dstptr),y
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inc <lzsa_srcptr + 0
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!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) {
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bne .skip1
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inc <lzsa_srcptr + 1
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.skip1: inc <lzsa_dstptr + 0
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bne .skip2
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inc <lzsa_dstptr + 1
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.skip2:
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} else {
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beq .incsrc2
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.resume_src2:
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inc <lzsa_dstptr + 0
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beq .incdst
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.resume_dst:
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}
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dex
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bne .cp_page
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dec <lzsa_length ; Any full pages left to copy?
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bne .cp_page
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} else {
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.got_cp_len: tay ; Check the lo-byte of length.
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beq .cp_page
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inx ; Increment # of pages to copy.
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.get_cp_src: clc ; Calc address of partial page.
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adc <lzsa_srcptr + 0
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sta <lzsa_srcptr + 0
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bcs .get_cp_dst
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dec <lzsa_srcptr + 1
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.get_cp_dst: tya
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clc ; Calc address of partial page.
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adc <lzsa_dstptr + 0
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sta <lzsa_dstptr + 0
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bcs .get_cp_idx
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dec <lzsa_dstptr + 1
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.get_cp_idx: tya ; Negate the lo-byte of length.
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eor #$FF
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tay
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iny
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.cp_page: lda (lzsa_srcptr),y
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sta (lzsa_dstptr),y
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iny
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bne .cp_page
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inc <lzsa_srcptr + 1
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inc <lzsa_dstptr + 1
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dex ; Any full pages left to copy?
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bne .cp_page
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}
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!if LZSA_SWAP_XZY {
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;
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; Shorter and faster path with NEW order of bits.
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;
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; STD NEW
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; ================================
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; xyz xzy
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; 00z 0z0 5-bit offset
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; 01z 0z1 9-bit offset
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; 10z 1z0 13-bit offset
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; 110 101 16-bit offset
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; 111 111 repeat offset
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; NVZ for a BIT instruction
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;
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; N.B. Saves 3 bytes in code length.
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; get5 and get13 are 8 cycles faster.
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; get9, get16, and rep are 4 cycles faster.
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;
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.lz_offset: lda #$20 ; Y bit in lzsa_cmdbuf.
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bit <lzsa_cmdbuf
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bmi .get_13_16_rep
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bne .get_9_bits
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.get_5_bits: dex ; X=$FF
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.get_13_bits: +LZSA_GET_NIBL ; Always returns with CS.
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bvc .get_5_skip
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clc
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.get_5_skip: rol ; Shift into position, set C.
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cpx #$00 ; X=$FF for a 5-bit offset.
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bne .set_offset
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sbc #2 ; Subtract 512 because 13-bit
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tax ; offset starts at $FE00.
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bne .get_low8 ; Always NZ from previous TAX.
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.get_9_bits: dex ; X=$FF if VC, X=$FE if VS.
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bvc .get_low8
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dex
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bvs .get_low8 ; Always VS from previous BIT.
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.get_13_16_rep: beq .get_13_bits ; Shares code with 5-bit path.
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.get_16_rep: bvs .lz_length ; Repeat previous offset.
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} else {
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;
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; Slower and longer path with STD order of bits.
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;
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; STD NEW
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; ================================
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; xyz xzy
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; 00z 0z0 5-bit offset
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; 01z 0z1 9-bit offset
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; 10z 1z0 13-bit offset
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; 110 101 16-bit offset
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; 111 111 repeat offset
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; NVZ for a BIT instruction
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;
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; N.B. Costs 3 bytes in code length.
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; get5 and get13 are 8 cycles slower.
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; get9, get16, and rep are 4 cycles slower.
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;
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.lz_offset: lda <lzsa_cmdbuf
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asl
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bcs .get_13_16_rep
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asl
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bcs .get_9_bits
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.get_5_bits: dex ; X=$FF
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.get_13_bits: asl
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php
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+LZSA_GET_NIBL ; Always returns with CS.
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plp
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rol ; Shift into position, set C.
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eor #$01
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cpx #$00 ; X=$FF for a 5-bit offset.
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bne .set_offset
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sbc #2 ; Subtract 512 because 13-bit
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; offset starts at $FE00.
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bne .get_low8x ; Always NZ from previous SBC.
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.get_9_bits: dex ; X=$FF if CS, X=$FE if CC.
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asl
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bcc .get_low8
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dex
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bcs .get_low8 ; Always VS from previous BIT.
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.get_13_16_rep: asl
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bcc .get_13_bits ; Shares code with 5-bit path.
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.get_16_rep: bmi .lz_length ; Repeat previous offset.
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}
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;
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; Copy bytes from decompressed window.
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;
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; N.B. X=0 is expected and guaranteed when we get here.
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;
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.get_16_bits: jsr lzsa2_get_byte ; Get hi-byte of offset.
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.get_low8x: tax
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.get_low8:
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!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) {
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+LZSA_GET_SRC ; Get lo-byte of offset.
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} else {
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lda (lzsa_srcptr),y
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inc <lzsa_srcptr + 0
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beq .incsrc3
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.resume_src3:
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}
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.set_offset: stx <lzsa_offset + 1 ; Save new offset.
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sta <lzsa_offset + 0
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.lz_length: ldx #$00 ; Hi-byte of length.
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lda <lzsa_cmdbuf
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and #$07
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clc
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adc #$02
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cmp #$09 ; Extended length?
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bne .got_lz_len
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inx
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jsr .get_length ; X=1 table index for match.
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.got_lz_len: eor #$FF ; Negate the lo-byte of length
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tay ; and check for zero.
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iny
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beq .calc_lz_addr
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eor #$FF
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inx ; Increment # of pages to copy.
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clc ; Calc destination for partial
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adc <lzsa_dstptr + 0 ; page.
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sta <lzsa_dstptr + 0
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bcs .calc_lz_addr
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dec <lzsa_dstptr + 1
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.calc_lz_addr: clc ; Calc address of match.
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lda <lzsa_dstptr + 0 ; N.B. Offset is negative!
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adc <lzsa_offset + 0
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sta <lzsa_winptr + 0
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lda <lzsa_dstptr + 1
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adc <lzsa_offset + 1
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sta <lzsa_winptr + 1
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.lz_page: lda (lzsa_winptr),y
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sta (lzsa_dstptr),y
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iny
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bne .lz_page
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inc <lzsa_winptr + 1
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inc <lzsa_dstptr + 1
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dex ; Any full pages left to copy?
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bne .lz_page
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jmp .cp_length ; Loop around to the beginning.
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!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) = 0 {
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.incsrc3:
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inc <lzsa_srcptr + 1
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bne .resume_src3 ; always taken
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}
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;
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; Lookup tables to differentiate literal and match lengths.
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;
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.nibl_len_tbl: !byte 3 + $10 ; 0+3 (for literal).
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!byte 9 + $10 ; 2+7 (for match).
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.byte_len_tbl: !byte 18 - 1 ; 0+3+15 - CS (for literal).
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!byte 24 - 1 ; 2+7+15 - CS (for match).
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;
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; Get 16-bit length in X:A register pair.
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;
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.get_length: +LZSA_GET_NIBL
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cmp #$FF ; Extended length?
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bcs .byte_length
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adc .nibl_len_tbl,x ; Always CC from previous CMP.
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.got_length: ldx #$00 ; Set hi-byte of 4 & 8 bit
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rts ; lengths.
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.byte_length: jsr lzsa2_get_byte ; So rare, this can be slow!
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adc .byte_len_tbl,x ; Always CS from previous CMP.
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bcc .got_length
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beq .finished
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!if LZSA_SWAP_LEN16 {
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.word_length: jsr lzsa2_get_byte ; So rare, this can be slow!
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tax
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} else {
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.word_length: jsr lzsa2_get_byte ; So rare, this can be slow!
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pha
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jsr lzsa2_get_byte ; So rare, this can be slow!
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tax
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pla
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rts
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}
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lzsa2_get_byte:
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lda (lzsa_srcptr),y ; Subroutine version for when
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inc <lzsa_srcptr + 0 ; inlining isn't advantageous.
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beq lzsa2_next_page
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rts
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lzsa2_next_page:
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inc <lzsa_srcptr + 1 ; Inc & test for bank overflow.
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!if LZSA_FROM_BANK {
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bmi lzsa2_next_bank ; Change for target hardware!
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}
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rts
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.finished: pla ; Decompression completed, pop
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pla ; return address.
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rts
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;
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; Get a nibble value from compressed data in A.
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;
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!if (LZSA_SLOW_NIBL | LZSA_SMALL_SIZE) {
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lzsa2_get_nibble:
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lsr <lzsa_nibflg ; Is there a nibble waiting?
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lda <lzsa_nibble ; Extract the lo-nibble.
|
|
bcs .got_nibble
|
|
|
|
inc <lzsa_nibflg ; Reset the flag.
|
|
!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) {
|
|
|
|
+LZSA_GET_SRC
|
|
|
|
} else {
|
|
|
|
lda (lzsa_srcptr),y
|
|
inc <lzsa_srcptr + 0
|
|
beq .incsrc4
|
|
.resume_src4:
|
|
|
|
}
|
|
|
|
sta <lzsa_nibble ; Preserve for next time.
|
|
lsr ; Extract the hi-nibble.
|
|
lsr
|
|
lsr
|
|
lsr
|
|
|
|
!if LZSA_SWAP_XZY {
|
|
sec ; Offset code relies on CS.
|
|
}
|
|
|
|
.got_nibble: ora #$F0
|
|
rts
|
|
|
|
} else {
|
|
|
|
lzsa2_new_nibble:
|
|
inc <lzsa_nibflg ; Reset the flag.
|
|
!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) {
|
|
|
|
+LZSA_GET_SRC
|
|
|
|
} else {
|
|
|
|
lda (lzsa_srcptr),y
|
|
inc <lzsa_srcptr + 0
|
|
beq .incsrc4
|
|
.resume_src4:
|
|
|
|
}
|
|
|
|
sta <lzsa_nibble ; Preserve for next time.
|
|
lsr ; Extract the hi-nibble.
|
|
lsr
|
|
lsr
|
|
lsr
|
|
|
|
!if LZSA_SWAP_XZY {
|
|
sec ; Offset code relies on CS.
|
|
}
|
|
|
|
rts
|
|
|
|
}
|
|
|
|
!if (LZSA_FROM_BANK | LZSA_NO_INLINE | LZSA_USE_FFFF) = 0 {
|
|
|
|
.incsrc4:
|
|
inc <lzsa_srcptr + 1
|
|
bne .resume_src4 ; always taken
|
|
|
|
}
|