lzsa/asm/x86/decompress_small_v2.asm
2020-01-13 18:14:11 +00:00

182 lines
6.6 KiB
NASM

; decompress_small_v2.asm - space-efficient decompressor implementation for x86
;
; 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.
segment .text
bits 32
; ---------------------------------------------------------------------------
; Decompress raw LZSA2 block
; inputs:
; * esi: raw LZSA2 block
; * edi: output buffer
; output:
; * eax: decompressed size
; ---------------------------------------------------------------------------
%ifndef BIN
global lzsa2_decompress
global _lzsa2_decompress
%endif
lzsa2_decompress:
_lzsa2_decompress:
pushad
;mov edi, [esp+32+4] ; edi = outbuf
;mov esi, [esp+32+8] ; esi = inbuf
xor ecx, ecx
xor ebx, ebx ; ebx = 0100H
inc bh
xor ebp, ebp
.decode_token:
mul ecx
lodsb ; read token byte: XYZ|LL|MMMM
mov dl, al ; keep token in dl
and al, 018H ; isolate literals length in token (LL)
shr al, 3 ; shift literals length into place
cmp al, 03H ; LITERALS_RUN_LEN_V2?
jne .got_literals ; no, we have the full literals count from the token, go copy
call .get_nibble ; get extra literals length nibble
add al, cl ; add len from token to nibble
cmp al, 012H ; LITERALS_RUN_LEN_V2 + 15 ?
jne .got_literals ; if not, we have the full literals count, go copy
lodsb ; grab extra length byte
add al,012H ; overflow?
jnc .got_literals ; if not, we have the full literals count, go copy
lodsw ; grab 16-bit extra length
.got_literals:
xchg ecx, eax
rep movsb ; copy ecx literals from esi to edi
test dl, 0C0h ; check match offset mode in token (X bit)
js .rep_match_or_large_offset
;;cmp dl,040H ; check if this is a 5 or 9-bit offset (Y bit)
; discovered via the test with bit 6 set
xchg ecx, eax ; clear ah - cx is zero from the rep movsb above
jne .offset_9_bit
; 5 bit offset
cmp dl, 020H ; test bit 5
call .get_nibble_x
jmp .dec_offset_top
.offset_9_bit: ; 9 bit offset
lodsb ; get 8 bit offset from stream in A
dec ah ; set offset bits 15-8 to 1
test dl, 020H ; test bit Z (offset bit 8)
je .get_match_length
.dec_offset_top:
dec ah ; clear bit 8 if Z bit is clear
; or set offset bits 15-8 to 1
jmp .get_match_length
.rep_match_or_large_offset:
;;cmp dl,0c0H ; check if this is a 13-bit offset or a 16-bit offset/rep match (Y bit)
jpe .rep_match_or_16_bit
; 13 bit offset
cmp dl, 0A0H ; test bit 5 (knowing that bit 7 is also set)
xchg ah, al
call .get_nibble_x
sub al, 2 ; substract 512
jmp .get_match_length_1
.rep_match_or_16_bit:
test dl, 020H ; test bit Z (offset bit 8)
jne .repeat_match ; rep-match
; 16 bit offset
lodsb ; Get 2-byte match offset
.get_match_length_1:
xchg ah, al
lodsb ; load match offset bits 0-7
.get_match_length:
xchg ebp, eax ; ebp: offset
.repeat_match:
xchg eax, edx ; ax: original token
and al, 07H ; isolate match length in token (MMM)
add al, 2 ; add MIN_MATCH_SIZE_V2
cmp al, 09H ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
jne .got_matchlen ; no, we have the full match length from the token, go copy
call .get_nibble ; get extra literals length nibble
add al, cl ; add len from token to nibble
cmp al, 018H ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
jne .got_matchlen ; no, we have the full match length from the token, go copy
lodsb ; grab extra length byte
add al,018H ; overflow?
jnc .got_matchlen ; if not, we have the entire length
je .done_decompressing ; detect EOD code
lodsw ; grab 16-bit length
.got_matchlen:
xchg ecx, eax ; copy match length into ecx
xchg esi, eax
movsx ebp, bp ; sign-extend bp to 32-bits
lea esi,[ebp+edi] ; esi now points at back reference in output data
rep movsb ; copy match
xchg esi, eax ; restore esi
jmp .decode_token ; go decode another token
.done_decompressing:
sub edi, [esp+32+4]
mov [esp+28], edi
popad
ret ; done
.get_nibble_x:
cmc ; carry set if bit 4 was set
rcr al, 1
call .get_nibble ; get nibble for offset bits 0-3
or al, cl ; merge nibble
rol al, 1
xor al, 0E1H ; set offset bits 7-5 to 1
ret
.get_nibble:
neg bh ; nibble ready?
jns .has_nibble
xchg ebx, eax
lodsb ; load two nibbles
xchg ebx, eax
.has_nibble:
mov cl, 4 ; swap 4 high and low bits of nibble
ror bl, cl
mov cl, 0FH
and cl, bl
ret