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Unpack raw blocks in 8088 decompressor

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emmanuel-marty 2019-04-03 13:05:32 +02:00
parent 18fc4da994
commit 0744ec99de
2 changed files with 4 additions and 12 deletions
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2
README.md
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@ -20,7 +20,7 @@ Performance over well-known compression corpus files:
Large 11159482 3771025 (33,79%) 3649821 (32,70%)
enwik9 1000000000 371841591 (37,18%) 355429941 (35,54%)
As an example of LZSA's simplicity, a size-optimized decompressor on 8088 has been implemented in 105 bytes.
As an example of LZSA's simplicity, a size-optimized decompressor on 8088 has been implemented in 91 bytes.
The compressor is approximately 2X slower than LZ4_HC but compresses better while maintaining similar decompression speeds and decompressor simplicity.

14
asm/8088/decompress_small.S
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@ -22,9 +22,9 @@
bits 16
; ---------------------------------------------------------------------------
; Decompress LZSA frame
; Decompress raw LZSA block
; inputs:
; * ds:si: LZSA frame
; * ds:si: raw LZSA block
; * es:di: output buffer
; output:
; * ax: decompressed size
@ -33,12 +33,6 @@
lzsa_decompress:
push di ; remember decompression offset
cld ; make string operations (lods, movs, stos..) move forward
lodsw ; grab first 2 bytes of block size
mov bp,ax ; keep block size in dx
lodsb ; grab last byte of block size / compression flag
test al,al ; if the compressed data is larger than 65,535 bytes, or if it is uncompressed, bail
jne .done_decompressing
add bp,si ; point at the end of the compressed data
xor cx,cx
@ -60,9 +54,6 @@ lzsa_decompress:
.copy_literals:
rep movsb ; copy cx literals from ds:si to es:di
cmp si,bp ; did we reach the end of the compressed data?
je .done_decompressing ; we did, bail. the last token does not include a match copy
test dl,dl ; check match offset size in token (O bit, ie. bit 7, the sign bit)
js .get_long_offset
@ -75,6 +66,7 @@ lzsa_decompress:
.get_match_length:
inc ax ; the match offset is stored off-by-1, increase it
je short .done_decompressing ; bail if we hit EOD
xchg ax,dx ; dx: match offset ax: original token
and al,0FH ; isolate match length in token (MMMM)