mirror of
https://github.com/emmanuel-marty/lzsa.git
synced 2024-11-25 10:30:45 +00:00
121 lines
4.5 KiB
ArmAsm
Executable File
121 lines
4.5 KiB
ArmAsm
Executable File
; decompress_small.S - space-efficient decompressor implementation for 8088
|
|
;
|
|
; 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 16
|
|
|
|
; ---------------------------------------------------------------------------
|
|
; Decompress raw LZSA1 block
|
|
; inputs:
|
|
; * ds:si: raw LZSA1 block
|
|
; * es:di: output buffer
|
|
; output:
|
|
; * ax: decompressed size
|
|
; ---------------------------------------------------------------------------
|
|
|
|
lzsa1_decompress:
|
|
push di ; remember decompression offset
|
|
cld ; make string operations (lods, movs, stos..) move forward
|
|
|
|
xor cx,cx
|
|
|
|
.decode_token:
|
|
mov ax,cx ; clear ah - cx is zero from above or from after rep movsb in .copy_match
|
|
lodsb ; read token byte: O|LLL|MMMM
|
|
mov dx,ax ; keep token in dl
|
|
|
|
and al,070H ; isolate literals length in token (LLL)
|
|
mov cl,4
|
|
shr al,cl ; shift literals length into place
|
|
|
|
cmp al,07H ; LITERALS_RUN_LEN?
|
|
jne .got_literals ; no, we have the full literals count from the token, go copy
|
|
|
|
lodsb ; grab extra length byte
|
|
add al,07H ; add LITERALS_RUN_LEN
|
|
jnc .got_literals ; if no overflow, we have the full literals count, go copy
|
|
jne .mid_literals
|
|
|
|
lodsw ; grab 16-bit extra length
|
|
db 81H ; mask inc ah/lodsb
|
|
; (*like jmp short .got_literals but faster)
|
|
|
|
.mid_literals:
|
|
inc ah ; add 256
|
|
lodsb ; grab single extra length byte
|
|
|
|
.got_literals:
|
|
xchg cx,ax
|
|
rep movsb ; copy cx literals from ds:si to es:di
|
|
|
|
test dl,dl ; check match offset size in token (O bit)
|
|
js .get_long_offset
|
|
|
|
dec cx
|
|
xchg cx,ax ; ah to 0xff - cx was zero from the rep movsb above
|
|
lodsb
|
|
db 3CH ; mask lodsw
|
|
; (*like jmp short .get_match_length but faster)
|
|
|
|
.get_long_offset:
|
|
lodsw ; Get 2-byte match offset
|
|
|
|
.get_match_length:
|
|
xchg dx,ax ; dx: match offset ax: original token
|
|
and al,0FH ; isolate match length in token (MMMM)
|
|
add al,3 ; add MIN_MATCH_SIZE
|
|
|
|
cmp al,012H ; MATCH_RUN_LEN?
|
|
jne .got_matchlen ; no, we have the full match length from the token, go copy
|
|
|
|
lodsb ; grab extra length byte
|
|
add al,012H ; add MIN_MATCH_SIZE + MATCH_RUN_LEN
|
|
jnc .got_matchlen ; if no overflow, we have the entire length
|
|
jne .mid_matchlen
|
|
|
|
lodsw ; grab 16-bit length
|
|
test ax,ax ; bail if we hit EOD
|
|
je short .done_decompressing
|
|
|
|
db 81H ; mask inc ah/lodsb
|
|
; (*like jmp short .got_literals but faster)
|
|
.mid_matchlen:
|
|
inc ah ; add 256
|
|
lodsb ; grab single extra length byte
|
|
|
|
.got_matchlen:
|
|
xchg cx,ax ; copy match length into cx
|
|
push ds ; save ds:si (current pointer to compressed data)
|
|
xchg si,ax
|
|
push es
|
|
pop ds
|
|
mov si,di ; ds:si now points at back reference in output data
|
|
add si,dx
|
|
rep movsb ; copy match
|
|
xchg si,ax ; restore ds:si
|
|
pop ds
|
|
jmp short .decode_token ; go decode another token
|
|
|
|
.done_decompressing:
|
|
pop ax ; retrieve the original decompression offset
|
|
xchg ax,di ; compute decompressed size
|
|
sub ax,di
|
|
ret ; done
|