Speed optimized version based on the original code by Emmanuel Marty. Reformatted.
Removed (unchanged) V1 decompressor source.
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Copyright (c) 2021 Emmanuel Marty
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Copyright (c) 2023 Emmanuel Marty, Chris Hodges
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This software is provided 'as-is', without any express or implied warranty. In
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no event will the authors be held liable for any damages arising from the use of
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@ -1,75 +0,0 @@
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; unzx0_68000.s - ZX0 decompressor for 68000 - 86 bytes
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;
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; in: a0 = start of compressed data
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; a1 = start of decompression buffer
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;
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; Copyright (C) 2021 Emmanuel Marty
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; ZX0 compression (c) 2021 Einar Saukas, https://github.com/einar-saukas/ZX0
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;
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; This software is provided 'as-is', without any express or implied
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; warranty. In no event will the authors be held liable for any damages
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; arising from the use of this software.
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;
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; Permission is granted to anyone to use this software for any purpose,
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; including commercial applications, and to alter it and redistribute it
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; freely, subject to the following restrictions:
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;
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; 1. The origin of this software must not be misrepresented; you must not
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; claim that you wrote the original software. If you use this software
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; in a product, an acknowledgment in the product documentation would be
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; appreciated but is not required.
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; 2. Altered source versions must be plainly marked as such, and must not be
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; misrepresented as being the original software.
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; 3. This notice may not be removed or altered from any source distribution.
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zx0_decompress:
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movem.l a2/d2,-(sp) ; preserve registers
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moveq #-128,d1 ; initialize empty bit queue
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; plus bit to roll into carry
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moveq #-1,d2 ; initialize rep-offset to 1
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.literals: bsr.s .get_elias ; read number of literals to copy
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subq.l #1,d0 ; dbf will loop until d0 is -1, not 0
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.copy_lits: move.b (a0)+,(a1)+ ; copy literal byte
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dbf d0,.copy_lits ; loop for all literal bytes
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add.b d1,d1 ; read 'match or rep-match' bit
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bcs.s .get_offset ; if 1: read offset, if 0: rep-match
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.rep_match: bsr.s .get_elias ; read match length (starts at 1)
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.do_copy: subq.l #1,d0 ; dbf will loop until d0 is -1, not 0
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.do_copy_offs: move.l a1,a2 ; calculate backreference address
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add.l d2,a2 ; (dest + negative match offset)
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.copy_match: move.b (a2)+,(a1)+ ; copy matched byte
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dbf d0,.copy_match ; loop for all matched bytes
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add.b d1,d1 ; read 'literal or match' bit
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bcc.s .literals ; if 0: go copy literals
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.get_offset: bsr.s .get_elias ; read high byte of match offset
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neg.b d0 ; obtain negative offset high byte
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beq.s .done ; exit if EOD marker
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move.w d0,d2 ; transfer negative high byte into d2
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lsl.w #8,d2 ; shift it to make room for low byte
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moveq #1,d0 ; initialize length value to 1
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move.b (a0)+,d2 ; read low byte of offset + 1 bit of len
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asr.l #1,d2 ; shift len bit into carry/offset in place
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bcs.s .do_copy_offs ; if len bit is set, no need for more
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bsr.s .elias_bt ; read rest of elias-encoded match length
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bra.s .do_copy_offs ; go copy match
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.get_elias: moveq #1,d0 ; initialize value to 1
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.elias_loop: add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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.got_bit: bcs.s .got_elias ; done if control bit is 1
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.elias_bt: add.b d1,d1 ; read data bit
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addx.l d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop ; keep reading
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.done: movem.l (sp)+,a2/d2 ; restore preserved registers
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.got_elias: rts
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@ -1,4 +1,4 @@
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A fast decompressor for the ZX0 format for 680x0 CPUs.
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An even faster decompressor for the ZX0 format for 680x0 CPUs.
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ZX0 by Einar Saukas, a successor to ZX7, reaches compression ratios in the ballpark of Exomizer, without requiring any decompression tables.
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157
unzx0_68000.S
157
unzx0_68000.S
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; unzx0_68000.s - ZX0 decompressor for 68000 - 88 bytes
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; unzx0_68000.s - ZX0 decompressor for 68000
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;
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; platon42: Modified to not preserve registers and to not use long word operations with
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; unlikely and unsupported block lengths > 64 KB. get_elias inlined for speed and other
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; optimizations.
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;
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; in: a0 = start of compressed data
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; a1 = start of decompression buffer
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;
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; out: a0 = end of compressed data
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; a1 = end of decompression buffer
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;
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; trashes: d0-d2/a2
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;
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; Copyright (C) 2021 Emmanuel Marty
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; Copyright (C) 2023 Emmanuel Marty, Chris Hodges
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; ZX0 compression (c) 2021 Einar Saukas, https://github.com/einar-saukas/ZX0
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;
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; This software is provided 'as-is', without any express or implied
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@ -23,54 +33,113 @@
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; 3. This notice may not be removed or altered from any source distribution.
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zx0_decompress:
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movem.l a2/d2,-(sp) ; preserve registers
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moveq #-128,d1 ; initialize empty bit queue
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; plus bit to roll into carry
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moveq #-1,d2 ; initialize rep-offset to 1
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moveq.l #-128,d1 ; initialize empty bit queue
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; plus bit to roll into carry
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moveq.l #-1,d2 ; initialize rep-offset to 1
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bra.s .literals
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.literals: bsr.s .get_elias ; read number of literals to copy
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subq.l #1,d0 ; dbf will loop until d0 is -1, not 0
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.copy_lits: move.b (a0)+,(a1)+ ; copy literal byte
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dbf d0,.copy_lits ; loop for all literal bytes
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add.b d1,d1 ; read 'match or rep-match' bit
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bcs.s .get_offset ; if 1: read offset, if 0: rep-match
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.do_copy_offs2
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move.b (a1,d2.l),(a1)+
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move.b (a1,d2.l),(a1)+
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.rep_match: bsr.s .get_elias ; read match length (starts at 1)
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.do_copy: subq.l #1,d0 ; dbf will loop until d0 is -1, not 0
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.do_copy_offs: move.l a1,a2 ; calculate backreference address
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add.l d2,a2 ; (dest + negative match offset)
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.copy_match: move.b (a2)+,(a1)+ ; copy matched byte
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dbf d0,.copy_match ; loop for all matched bytes
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add.b d1,d1 ; read 'literal or match' bit
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bcs.s .get_offset ; if 0: go copy literals
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add.b d1,d1 ; read 'literal or match' bit
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bcc.s .literals ; if 0: go copy literals
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.literals
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; read number of literals to copy
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moveq.l #1,d0 ; initialize value to 1
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.elias_loop1
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add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit1 ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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.get_offset: moveq #-2,d0 ; initialize value to $fe
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bsr.s .elias_loop ; read high byte of match offset
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addq.b #1,d0 ; obtain negative offset high byte
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beq.s .done ; exit if EOD marker
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move.w d0,d2 ; transfer negative high byte into d2
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lsl.w #8,d2 ; shift it to make room for low byte
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.got_bit1
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bcs.s .got_elias1 ; done if control bit is 1
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add.b d1,d1 ; read data bit
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addx.w d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop1 ; keep reading
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moveq #1,d0 ; initialize length value to 1
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move.b (a0)+,d2 ; read low byte of offset + 1 bit of len
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asr.l #1,d2 ; shift len bit into carry/offset in place
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bcs.s .do_copy_offs ; if len bit is set, no need for more
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bsr.s .elias_bt ; read rest of elias-encoded match length
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bra.s .do_copy_offs ; go copy match
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.got_elias1
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subq.w #1,d0 ; dbf will loop until d0 is -1, not 0
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.copy_lits
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move.b (a0)+,(a1)+ ; copy literal byte
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dbra d0,.copy_lits ; loop for all literal bytes
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.get_elias: moveq #1,d0 ; initialize value to 1
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.elias_loop: add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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add.b d1,d1 ; read 'match or rep-match' bit
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bcs.s .get_offset ; if 1: read offset, if 0: rep-match
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.got_bit: bcs.s .got_elias ; done if control bit is 1
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.elias_bt: add.b d1,d1 ; read data bit
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addx.l d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop ; keep reading
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.rep_match
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; read match length (starts at 1)
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moveq.l #1,d0 ; initialize value to 1
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.elias_loop2
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add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit2 ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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.done: movem.l (sp)+,a2/d2 ; restore preserved registers
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.got_elias: rts
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.got_bit2
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bcs.s .got_elias2 ; done if control bit is 1
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add.b d1,d1 ; read data bit
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addx.w d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop2 ; keep reading
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.got_elias2
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subq.w #1,d0 ; dbra will loop until d0 is -1, not 0
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.do_copy_offs
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move.l a1,a2 ; calculate backreference address
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add.l d2,a2 ; (dest + negative match offset)
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.copy_match
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move.b (a2)+,(a1)+ ; copy matched byte
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dbra d0,.copy_match ; loop for all matched bytes
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add.b d1,d1 ; read 'literal or match' bit
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bcc.s .literals ; if 0: go copy literals
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.get_offset
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moveq.l #-2,d0 ; initialize value to $fe
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; read high byte of match offset
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.elias_loop3
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add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit3 ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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.got_bit3
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bcs.s .got_elias3 ; done if control bit is 1
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add.b d1,d1 ; read data bit
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addx.w d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop3 ; keep reading
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.got_elias3
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addq.b #1,d0 ; obtain negative offset high byte
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beq.s .done ; exit if EOD marker
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move.b d0,-(sp) ; transfer negative high byte to stack
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move.w (sp)+,d2 ; shift it to make room for low byte
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move.b (a0)+,d2 ; read low byte of offset + 1 bit of len
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asr.l #1,d2 ; shift len bit into carry/offset in place
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bcs.s .do_copy_offs2 ; if len bit is set, no need for more
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moveq.l #1,d0 ; initialize length value to 1
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; read rest of elias-encoded match length
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add.b d1,d1 ; read data bit
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addx.w d0,d0 ; shift data bit into value in d0
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.elias_loop4
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add.b d1,d1 ; shift bit queue, high bit into carry
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bne.s .got_bit4 ; queue not empty, bits remain
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move.b (a0)+,d1 ; read 8 new bits
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addx.b d1,d1 ; shift bit queue, high bit into carry
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; and shift 1 from carry into bit queue
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.got_bit4
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bcs.s .do_copy_offs ; done if control bit is 1
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add.b d1,d1 ; read data bit
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addx.w d0,d0 ; shift data bit into value in d0
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bra.s .elias_loop4 ; keep reading
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.done
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rts
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