mirror of
https://github.com/emmanuel-marty/lzsa.git
synced 2024-11-25 10:30:45 +00:00
182 lines
6.6 KiB
NASM
182 lines
6.6 KiB
NASM
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; decompress_small_v2.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 LZSA2 block
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; inputs:
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; * esi: raw LZSA2 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 lzsa2_decompress
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global _lzsa2_decompress
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%endif
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lzsa2_decompress:
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_lzsa2_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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xor ebx, ebx ; ebx = 0100H
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inc bh
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xor ebp, ebp
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.decode_token:
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mul ecx
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lodsb ; read token byte: XYZ|LL|MMMM
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mov dl, al ; keep token in dl
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and al, 018H ; isolate literals length in token (LL)
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shr al, 3 ; shift literals length into place
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cmp al, 03H ; LITERALS_RUN_LEN_V2?
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jne .got_literals ; no, we have the full literals count from the token, go copy
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call .get_nibble ; get extra literals length nibble
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add al, cl ; add len from token to nibble
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cmp al, 012H ; LITERALS_RUN_LEN_V2 + 15 ?
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jne .got_literals ; if not, we have the full literals count, go copy
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lodsb ; grab extra length byte
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add al,012H ; overflow?
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jnc .got_literals ; if not, we have the full literals count, go copy
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lodsw ; grab 16-bit extra length
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.got_literals:
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xchg ecx, eax
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rep movsb ; copy ecx literals from esi to edi
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test dl, 0C0h ; check match offset mode in token (X bit)
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js .rep_match_or_large_offset
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;;cmp dl,040H ; check if this is a 5 or 9-bit offset (Y bit)
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; discovered via the test with bit 6 set
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xchg ecx, eax ; clear ah - cx is zero from the rep movsb above
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jne .offset_9_bit
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; 5 bit offset
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cmp dl, 020H ; test bit 5
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call .get_nibble_x
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jmp .dec_offset_top
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.offset_9_bit: ; 9 bit offset
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lodsb ; get 8 bit offset from stream in A
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dec ah ; set offset bits 15-8 to 1
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test dl, 020H ; test bit Z (offset bit 8)
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je .get_match_length
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.dec_offset_top:
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dec ah ; clear bit 8 if Z bit is clear
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; or set offset bits 15-8 to 1
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jmp .get_match_length
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.rep_match_or_large_offset:
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;;cmp dl,0c0H ; check if this is a 13-bit offset or a 16-bit offset/rep match (Y bit)
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jpe .rep_match_or_16_bit
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; 13 bit offset
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cmp dl, 0A0H ; test bit 5 (knowing that bit 7 is also set)
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xchg ah, al
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call .get_nibble_x
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sub al, 2 ; substract 512
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jmp .get_match_length_1
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.rep_match_or_16_bit:
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test dl, 020H ; test bit Z (offset bit 8)
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jne .repeat_match ; rep-match
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; 16 bit offset
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lodsb ; Get 2-byte match offset
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.get_match_length_1:
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xchg ah, al
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lodsb ; load match offset bits 0-7
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.get_match_length:
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xchg ebp, eax ; ebp: offset
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.repeat_match:
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xchg eax, edx ; ax: original token
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and al, 07H ; isolate match length in token (MMM)
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add al, 2 ; add MIN_MATCH_SIZE_V2
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cmp al, 09H ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
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jne .got_matchlen ; no, we have the full match length from the token, go copy
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call .get_nibble ; get extra literals length nibble
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add al, cl ; add len from token to nibble
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cmp al, 018H ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
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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,018H ; overflow?
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jnc .got_matchlen ; if not, we have the entire length
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je .done_decompressing ; detect EOD code
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lodsw ; grab 16-bit length
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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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movsx ebp, bp ; sign-extend bp to 32-bits
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lea esi,[ebp+edi] ; esi now points at back reference in output data
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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
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popad
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ret ; done
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.get_nibble_x:
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cmc ; carry set if bit 4 was set
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rcr al, 1
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call .get_nibble ; get nibble for offset bits 0-3
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or al, cl ; merge nibble
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rol al, 1
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xor al, 0E1H ; set offset bits 7-5 to 1
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ret
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.get_nibble:
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neg bh ; nibble ready?
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jns .has_nibble
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xchg ebx, eax
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lodsb ; load two nibbles
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xchg ebx, eax
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.has_nibble:
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mov cl, 4 ; swap 4 high and low bits of nibble
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ror bl, cl
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mov cl, 0FH
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and cl, bl
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ret
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