mirror of
https://github.com/emmanuel-marty/lzsa.git
synced 2024-11-22 21:32:07 +00:00
121 lines
4.3 KiB
NASM
121 lines
4.3 KiB
NASM
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; decompress_small_v1.asm - space-efficient decompressor implementation for x86
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;
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; Copyright (C) 2019 Emmanuel Marty
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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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segment .text
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bits 32
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; ---------------------------------------------------------------------------
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; Decompress raw LZSA1 block
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; inputs:
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; * esi: raw LZSA1 block
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; * edi: output buffer
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; output:
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; * eax: decompressed size
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; ---------------------------------------------------------------------------
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%ifndef BIN
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global lzsa1_decompress
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global _lzsa1_decompress
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%endif
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lzsa1_decompress:
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_lzsa1_decompress:
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pushad
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;mov edi, [esp+32+4] ; edi = outbuf
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;mov esi, [esp+32+8] ; esi = inbuf
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xor ecx, ecx
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.decode_token:
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mul ecx
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lodsb ; read token byte: O|LLL|MMMM
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mov dl, al ; keep token in dl
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and al, 070H ; isolate literals length in token (LLL)
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shr al, 4 ; shift literals length into place
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cmp al, 07H ; LITERALS_RUN_LEN?
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jne .got_literals ; no, we have the full literals count from the token, go copy
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lodsb ; grab extra length byte
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add al, 07H ; add LITERALS_RUN_LEN
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jnc .got_literals ; if no overflow, we have the full literals count, go copy
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jne .mid_literals
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lodsw ; grab 16-bit extra length
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jmp .got_literals
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.mid_literals:
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lodsb ; grab single extra length byte
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inc ah ; add 256
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.got_literals:
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xchg ecx, eax
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rep movsb ; copy cx literals from ds:si to es:di
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test dl, dl ; check match offset size in token (O bit)
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js .get_long_offset
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dec ecx
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xchg eax, ecx ; clear ah - cx is zero from the rep movsb above
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lodsb
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jmp .get_match_length
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.get_long_offset:
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lodsw ; Get 2-byte match offset
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.get_match_length:
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xchg eax, edx ; edx: match offset eax: original token
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and al, 0FH ; isolate match length in token (MMMM)
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add al, 3 ; add MIN_MATCH_SIZE
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cmp al, 012H ; MATCH_RUN_LEN?
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jne .got_matchlen ; no, we have the full match length from the token, go copy
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lodsb ; grab extra length byte
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add al,012H ; add MIN_MATCH_SIZE + MATCH_RUN_LEN
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jnc .got_matchlen ; if no overflow, we have the entire length
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jne .mid_matchlen
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lodsw ; grab 16-bit length
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test eax, eax ; bail if we hit EOD
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je .done_decompressing
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jmp .got_matchlen
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.mid_matchlen:
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lodsb ; grab single extra length byte
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inc ah ; add 256
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.got_matchlen:
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xchg ecx, eax ; copy match length into ecx
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xchg esi, eax
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mov esi, edi ; esi now points at back reference in output data
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movsx edx, dx ; sign-extend dx to 32-bits.
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add esi, edx
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rep movsb ; copy match
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xchg esi, eax ; restore esi
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jmp .decode_token ; go decode another token
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.done_decompressing:
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sub edi, [esp+32+4]
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mov [esp+28], edi ; eax = decompressed size
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popad
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ret ; done
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