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Merge pull request #35 from MobyGamer/decompressor/8086_speed_jumptable

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Rewrite 8088 jumptable decompressor for maximum speed
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Emmanuel Marty 2019-10-27 10:28:48 +01:00 committed by GitHub
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asm/8088/LZSA1JMP.ASM
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@ -1,32 +1,125 @@
; lzsa1fta.asm time-efficient decompressor implementation for 8086 CPUs.
; Turbo Assembler IDEAL mode dialect; can also be assembled with NASM.
; lzsa1fta.asm time-efficient decompressor implementation for 808x CPUs.
; Turbo Assembler IDEAL mode dialect.
; (Is supposed to also assemble with NASM's IDEAL mode support, but YMMV.)
;
; Usual DOS assembler SMALL model assumptions apply. This code:
; - Assumes it was invoked via NEAR call (change RET to RETF for FAR calls)
; - Is interrupt-safe
; - Is not re-entrant (do not decompress while already running decompression)
; - Trashes all data and segment registers
; This code assembles to about 3K of lookup tables and unrolled code,
; but the tradeoff for that size is the absolute fastest decompressor
; of LZSA1 block data for 808x CPUs.
; If you need moderately fast code with less size, see LZSA1FTA.ASM.
; If you need the smallest decompression code, see decompress_small_v1.S.
;
; Copyright (C) 2019 Jim Leonard, Emmanuel Marty
; Usual DOS assembler SMALL model assumptions apply. This code:
; - Assumes it was invoked via NEAR call (change RET to RETF for FAR calls)
; - Is interrupt-safe
; - Is not re-entrant (do not decompress while already running decompression)
; - Trashes all data and segment registers
;
; 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.
; Copyright (C) 2019 Jim Leonard, Emmanuel Marty
;
; 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:
; 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.
;
; 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.
; 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.
;
; ===========================================================================
;
; The key area to concentrate on when optimizing LZSA1 decompression speed is
; reducing time spent handling the shortest matches. This is for two reasons:
; 1. shorter matches are more common
; 2. short matches are least efficient in terms of decomp speed per byte
; You can confirm #1 using the --stats mode of the compressor.
;
; Branches are costly on 8086. To ensure we branch as little as possible, a
; jumptable will be used to branch directly to as many direct decode paths as
; possible. This will burn up 512 bytes of RAM for a jumptable, and a few
; hundred bytes of duplicated program code (rather than JMP/CALL common code
; blocks, we inline them to avoid the branch overhead).
;
; ===========================================================================
;
; === LZSA1 block reference:
;
; Blocks encoded as LZSA1 are composed from consecutive commands.
; Each command follows this format:
;
; token: <O|LLL|MMMM>
; optional extra literal length
; literal values
; match offset low
; optional match offset high
; optional extra encoded match length
;
;
; === LZSA1 Token Reference:
;
; 7 6 5 4 3 2 1 0
; O L L L M M M M
;
; L: 3-bit literals length (0-6, or 7 if extended). If the number of literals for
; this command is 0 to 6, the length is encoded in the token and no extra bytes
; are required. Otherwise, a value of 7 is encoded and extra bytes follow as
; 'optional extra literal length'
;
; M: 4-bit encoded match length (0-14, or 15 if extended). Likewise, if the
; encoded match length for this command is 0 to 14, it is directly stored,
; otherwise 15 is stored and extra bytes follow as 'optional extra encoded match
; length'. Except for the last command in a block, a command always contains a
; match, so the encoded match length is the actual match length, offset by the
; minimum which is 3 bytes. For instance, an actual match length of 10 bytes to
; be copied, is encoded as 7.
;
; O: set for a 2-bytes match offset, clear for a 1-byte match offset
;
;
; === Decoding extended literal length:
;
; If the literals length is 7 or more, then an extra byte follows here, with
; three possible values:
;
; 0-248: the value is added to the 7 stored in the token.
; 250: a second byte follows. The final literals value is 256 + the second byte.
; 249: a little-endian 16-bit value follows, forming the final literals value.
;
;
; === Decoding match offsets:
;
; match offset low: The low 8 bits of the match offset follows.
;
; optional match offset high: If the 'O' bit (bit 7) is set in the token, the
; high 8 bits of the match offset follow, otherwise they are understood to be all
; set to 1. For instance, a short offset of 0x70 is interpreted as 0xff70
;
;
; === Decoding extra encoded match length:
;
; optional extra encoded match length: If the encoded match length is 15 or more,
; the 'M' bits in the token form the value 15, and an extra byte follows here,
; with three possible types of value.
;
; 0-237: the value is added to the 15 stored in the token. The final value is 3 + 15 + this byte.
; 239: a second byte follows. The final match length is 256 + the second byte.
; 238: a second and third byte follow, forming a little-endian 16-bit value.
; The final encoded match length is that 16-bit value.
;
; ===========================================================================
IDEAL
P8086
IDEAL ; Use Turbo Assembler IDEAL syntax checking
P8086 ; Restrict code generation to the 808x and later
JUMPS ; Perform fixups for out-of-bound conditional jumps
; This is required for the (L=07 & M=0Fh) decode paths as they
; have the most code, but these are uncommon paths so the
; tiny speed loss in just these paths is not a concern.
SEGMENT CODE para public
@ -34,203 +127,385 @@ ASSUME cs:CODE, ds:CODE
PUBLIC lzsa1_decompress_speed_jumptable
; ---------------------------------------------------------------------------
; Decompress raw LZSA1 block
; inputs:
; * ds:si: raw LZSA1 block
; * es:di: output buffer
; output:
; * ax: decompressed size
; ---------------------------------------------------------------------------
; EQU helper statements (so we can construct a jump table without going crazy)
;Jump table for handling LLL bits in initial LZSA1 tokens.
;Previous code would SHR val,4 to get a count from 0 to 7, then rep movsb.
;We can overload the shift operation into a jump table that jumps directly
;to optimized copying routine for 0-7 bytes. Must declare in code segment.
;Note: If this looks strange for declaring a jump table, that's because it
;is a workaround for the Turbo Pascal harness that tests it. Turbo Pascal
;treats OFFSET (label) as a relocatble item and throws an error, so we fool
;it by building the table with absolute EQU/literals instead.
L0b EQU OFFSET check_offset_size
L1b EQU OFFSET copy1b
L2b EQU OFFSET copy2b
L3b EQU OFFSET copy3b
L4b EQU OFFSET copy4b
L5b EQU OFFSET copy5b
L6b EQU OFFSET copy6b
L7b EQU OFFSET need_length_byte
copytable DW L0b,L0b,L0b,L0b,L0b,L0b,L0b,L0b
DW L1b,L1b,L1b,L1b,L1b,L1b,L1b,L1b
DW L2b,L2b,L2b,L2b,L2b,L2b,L2b,L2b
DW L3b,L3b,L3b,L3b,L3b,L3b,L3b,L3b
DW L4b,L4b,L4b,L4b,L4b,L4b,L4b,L4b
DW L5b,L5b,L5b,L5b,L5b,L5b,L5b,L5b
DW L6b,L6b,L6b,L6b,L6b,L6b,L6b,L6b
DW L7b,L7b,L7b,L7b,L7b,L7b,L7b,L7b
minmatch EQU 3
litrunlen EQU 7
leml1 EQU OFFSET lit_ext_mat_len_1b
leme1 EQU OFFSET lit_ext_mat_ext_1b
leml2 EQU OFFSET lit_ext_mat_len_2b
leme2 EQU OFFSET lit_ext_mat_ext_2b
;short-circuit special cases for 0 through 6 literal copies:
l6ml1 EQU OFFSET lit_len_mat_len_1b
l6me1 EQU OFFSET lit_len_mat_ext_1b
l6ml2 EQU OFFSET lit_len_mat_len_2b
l6me2 EQU OFFSET lit_len_mat_ext_2b
l5ml1 EQU OFFSET lit_len_mat_len_1b + 1
l5me1 EQU OFFSET lit_len_mat_ext_1b + 1
l5ml2 EQU OFFSET lit_len_mat_len_2b + 1
l5me2 EQU OFFSET lit_len_mat_ext_2b + 1
l4ml1 EQU OFFSET lit_len_mat_len_1b + 2
l4me1 EQU OFFSET lit_len_mat_ext_1b + 2
l4ml2 EQU OFFSET lit_len_mat_len_2b + 2
l4me2 EQU OFFSET lit_len_mat_ext_2b + 2
l3ml1 EQU OFFSET lit_len_mat_len_1b + 3
l3me1 EQU OFFSET lit_len_mat_ext_1b + 3
l3ml2 EQU OFFSET lit_len_mat_len_2b + 3
l3me2 EQU OFFSET lit_len_mat_ext_2b + 3
l2ml1 EQU OFFSET lit_len_mat_len_1b + 4
l2me1 EQU OFFSET lit_len_mat_ext_1b + 4
l2ml2 EQU OFFSET lit_len_mat_len_2b + 4
l2me2 EQU OFFSET lit_len_mat_ext_2b + 4
l1ml1 EQU OFFSET lit_len_mat_len_1b + 5
l1me1 EQU OFFSET lit_len_mat_ext_1b + 5
l1ml2 EQU OFFSET lit_len_mat_len_2b + 5
l1me2 EQU OFFSET lit_len_mat_ext_2b + 5
l0ml1 EQU OFFSET lit_len_mat_len_1b + 6 ; MMMM handling comes after LLL code
l0me1 EQU OFFSET lit_len_mat_ext_1b + 6 ; MMMM handling comes after LLL code
l0ml2 EQU OFFSET lit_len_mat_len_2b + 6 ; MMMM handling comes after LLL code
l0me2 EQU OFFSET lit_len_mat_ext_2b + 6 ; MMMM handling comes after LLL code
; === Hand-written (!) jumptable actually begins here.
; Located before the program code results in an extra JMP and 3 wasted bytes,
; but it makes the code easier to follow in this location.
; Relocate the jump table after the ENDP directive to save 3 bytes.
;
; 7 6 5 4 3 2 1 0
; O L L L M M M M
;
; 0 1 2 3 4 5 6 7 8 9 a b c d e f
jtbl DW l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0ml1,l0me1 ;0
DW l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1ml1,l1me1 ;1
DW l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2ml1,l2me1 ;2
DW l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3ml1,l3me1 ;3
DW l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4ml1,l4me1 ;4
DW l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5ml1,l5me1 ;5
DW l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6ml1,l6me1 ;6
DW leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leml1,leme1 ;7
DW l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0ml2,l0me2 ;8
DW l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1ml2,l1me2 ;9
DW l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2ml2,l2me2 ;a
DW l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3ml2,l3me2 ;b
DW l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4ml2,l4me2 ;c
DW l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5ml2,l5me2 ;d
DW l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6ml2,l6me2 ;e
DW leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leml2,leme2 ;f
PROC lzsa1_decompress_speed_jumptable NEAR
; ---------------------------------------------------------------------------
; Decompress raw LZSA1 block
; inputs:
; * ds:si: raw LZSA1 block
; * es:di: output buffer
; output:
; * ax: decompressed size
; ---------------------------------------------------------------------------
MACRO get_byte_match_offset
mov ah,0ffh ;O=0, so set up offset's high byte
lodsb ;load low byte; ax=match offset
xchg bp,ax ;bp=match offset ax=00 + original token
ENDM
MACRO get_word_match_offset
lodsw ;ax=match offset
xchg bp,ax ;bp=match offset ax=00 + original token
ENDM
MACRO do_match_copy_long
LOCAL do_run, do_run_w
; Copies a long match as optimally as possible.
; requirements: cx=length, bp=negative offset, ds:si=compdata, es:di=output
; trashes: ax, bx
; must leave cx=0 at exit
mov bx,ds ;save ds
mov ax,es
mov ds,ax ;ds=es
xchg ax,si ;save si
lea si,[bp+di] ;si = output buffer + negative match offset
cmp bp,-2 ;do we have a byte/word run to optimize?
jae do_run ;perform a run if so, otherwise fall through
;You may be tempted to change "jae" to "jge" because DX is a signed number.
;Don't! The total window is 64k, so if you treat this as a signed comparison,
;you will get incorrect results for offsets over 32K.
;If we're here, we have a long copy and it isn't byte-overlapping (if it
;overlapped, we'd be in @@do_run) So, let's copy faster with REP MOVSW.
;This affects 8088 only slightly, but is a bigger win on 8086 and higher.
shr cx,1
rep movsw
adc cl,0
rep movsb
xchg si,ax ;restore si
mov ds,bx ;restore ds
jmp decode_token
do_run:
je do_run_w ;if applicable, handle word-sized value faster
xchg dx,ax ;save si into dx, as ax is getting trashed
lodsb ;load first byte of run into al
mov ah,al
shr cx,1
rep stosw ;perform word run
adc cl,0
rep stosb ;finish word run
mov si,dx ;restore si
mov ds,bx ;restore ds
jmp decode_token
do_run_w:
xchg dx,ax ;save si into dx, as ax is getting trashed
lodsw ;load first word of run
shr cx,1
rep stosw ;perform word run
adc cl,0 ;despite 2-byte offset, compressor might
rep stosb ;output odd length. better safe than sorry.
mov si,dx ;restore si
mov ds,bx ;restore ds
jmp decode_token
ENDM
MACRO do_match_copy
; Copies a shorter match with as little overhead as possible.
; requirements: cx=length, bp=negative offset, ds:si=compdata, es:di=output
; trashes: ax, bx
; must leave cx=0 at exit
mov bx,ds ;save ds
mov ax,es
mov ds,ax ;ds=es
xchg ax,si ;save si
lea si,[bp+di] ;si = output buffer + negative match offset
rep movsb
xchg si,ax ;restore si
mov ds,bx ;restore ds
jmp decode_token
ENDM
MACRO do_literal_copy
; Copies a literal sequence using words.
; Meant for longer lengths; for 128 bytes or less, use REP MOVSB.
; requirements: cx=length, ds:si=compdata, es:di=output
; must leave cx=0 at exit
shr cx,1
rep movsw
adc cl,0
rep movsb
ENDM
MACRO copy_small_match_len
and al,0FH ;isolate length in token (MMMM)
add al,minmatch ;ax=match length
xchg cx,ax ;cx=match length
do_match_copy ;copy match with cx=length, bp=offset
ENDM
MACRO copy_large_match_len
LOCAL val239, val238, EOD
; Handle MMMM=Fh
; Assumptions: ah=0 from get_????_match_offset's xchg
lodsb ;grab extra match length byte
add al,0Fh+minmatch ;add MATCH_RUN_LEN + MIN_MATCH_SIZE
jz val238 ;if zf & cf, 238: get 16-bit match length
jc val239 ;if cf, 239: get extra match length byte
xchg cx,ax ;otherwise, we have our match length
do_match_copy_long ;copy match with cx=length, bp=offset
val239:
lodsb ;ah=0; grab single extra length byte
inc ah ;ax=256+length byte
xchg cx,ax
do_match_copy_long ;copy match with cx=length, bp=offset
val238:
lodsw ;grab 16-bit length
xchg cx,ax
jcxz EOD ;is it the EOD marker? Exit if so
do_match_copy_long ;copy match with cx=length, bp=offset
EOD:
jmp done_decompressing
ENDM
lzsa1_start:
push di ;remember decompression offset
cld ;ensure string ops move forward
xor cx,cx
@@decode_token:
xchg cx,ax ;clear ah (cx = 0 from match copy's rep movsb)
decode_token:
xchg cx,ax ;clear ah (cx = 0 from match copy's REP)
lodsb ;read token byte: O|LLL|MMMM
mov dx,ax ;copy our token to dl for later MMMM handling
mov bp,ax ;preserve 0+token in bp for later MMMM handling
mov bx,ax ;prep for table lookup
shl bx,1 ;adjust for offset word size
jmp [cs:jtbl+bx] ;jump directly to relevant decode path
and al,070H ;isolate literals length in token (LLL)
jz check_offset_size ;if LLL=0, we have no literals; goto match
; There are eight basic decode paths for an LZSA1 token. Each of these
; paths perform only the necessary actions to decode the token and then
; fetch the next token. This results in a lot of code duplication, but
; it is the only way to get down to two branches per token (jump to unique
; decode path, then jump back to next token) for the most common cases.
; Jump to short copy routine for LLL=1 though 6, need_length_byte for LLL=7
mov bx,ax ;prep for table lookup (must copy, don't XCHG!)
jmp [cs:copytable+bx]
; Path #1: LLL=0-6, MMMM=0-Eh, O=0 (1-byte match offset)
; Handle LLL=0-6 by jumping directly into # of bytes to copy (6 down to 1)
lit_len_mat_len_1b:
movsb
movsb
movsb
movsb
movsb
movsb
get_byte_match_offset
copy_small_match_len
need_length_byte:
lodsb ;grab extra length byte
add al,07H ;add LITERALS_RUN_LEN
jnc @@got_literals_exact ;if no overflow, we have full count
je @@big_literals
@@mid_literals:
lodsb ;grab single extra length byte
inc ah ;add 256
xchg cx,ax ;with longer counts, we can save some time
shr cx,1 ;by doing a word copy instead of a byte copy.
rep movsw ;We don't need to account for overlap because
adc cx,0 ;source for literals isn't the output buffer.
rep movsb
jmp check_offset_size
; Path #2: LLL=0-6, MMMM=Fh, O=0 (1-byte match offset)
lit_len_mat_ext_1b:
movsb
movsb
movsb
movsb
movsb
movsb
get_byte_match_offset
copy_large_match_len
@@big_literals:
lodsw ;grab 16-bit extra length
xchg cx,ax ;with longer counts, we can save some time
shr cx,1 ;by doing a word copy instead of a byte copy.
rep movsw
adc cx,0
rep movsb
jmp check_offset_size
; Used for counts 7-248. In test data, average value around 1Ah. YMMV.
@@got_literals_exact:
; Path #3: LLL=7, MMMM=0-Eh, O=0 (1-byte match offset)
lit_ext_mat_len_1b:
; on entry: ax=0 + token, bp=ax
lodsb ;grab extra literal length byte
add al,litrunlen ;add 7h literal run length
jz @@val249_3 ;if zf & cf, 249: get 16-bit literal length
jc @@val250_3 ;if cf, 250: get extra literal length byte
xchg cx,ax ;otherwise, we have our literal length
do_literal_copy ;this might be better as rep movsw !!! benchmark
get_byte_match_offset
copy_small_match_len
@@val250_3:
lodsb ;ah=0; grab single extra length byte
inc ah ;ax=256+length byte
xchg cx,ax
rep movsb ;copy cx literals from ds:si to es:di
jmp check_offset_size
;Literal copy sequence for lengths 1-6:
copy6b: movsb
copy5b: movsb
copy4b: movsb
copy3b: movsb
copy2b: movsb
copy1b: movsb
;Literals done; fall through to match offset determination
check_offset_size:
test dl,dl ;check match offset size in token (O bit)
js @@get_long_offset ;load absolute 16-bit match offset
mov ah,0ffh ;set up high byte
lodsb ;load low byte
@@get_match_length:
xchg dx,ax ;dx: match offset ax: original token
and al,0FH ;isolate match length in token (MMMM)
cmp al,0FH ;MATCH_RUN_LEN?
jne @@got_matchlen_short ;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 @@do_long_copy ;if no overflow, we have the entire length
jne @@mid_matchlen
do_literal_copy
get_byte_match_offset
copy_small_match_len
@@val249_3:
lodsw ;grab 16-bit length
xchg cx,ax ;get ready to do a long copy
jcxz @@done_decompressing ;wait, is it the EOD marker? Exit if so
jmp @@copy_len_preset ;otherwise, do the copy
xchg cx,ax
do_literal_copy
get_byte_match_offset
copy_small_match_len
@@got_matchlen_short:
add al,3 ;add MIN_MATCH_SIZE
xchg cx,ax ;copy match length into cx
mov bp,ds ;save ds
mov ax,es
mov ds,ax ;ds=es
xchg ax,si ;save si
mov si,di ;ds:si now points at back reference in output data
add si,dx
rep movsb ;copy match
xchg si,ax ;restore si
mov ds,bp ;restore ds
jmp @@decode_token ;go decode another token
@@done_decompressing:
; Path #4: LLL=7, MMMM=Fh, O=0 (1-byte match offset)
lit_ext_mat_ext_1b:
; on entry: ax=0 + token, bp=ax
lodsb ;grab extra literal length byte
add al,litrunlen ;add 7h literal run length
jz @@val249_4 ;if zf & cf, 249: get 16-bit literal length
jc @@val250_4 ;if cf, 250: get extra literal length byte
xchg cx,ax ;otherwise, we have our literal length
do_literal_copy ;this might be better as rep movsw !!! benchmark
get_byte_match_offset
copy_large_match_len
@@val250_4:
lodsb ;ah=0; grab single extra length byte
inc ah ;ax=256+length byte
xchg cx,ax
do_literal_copy
get_byte_match_offset
copy_large_match_len
@@val249_4:
lodsw ;grab 16-bit length
xchg cx,ax
do_literal_copy
get_byte_match_offset
copy_large_match_len
; Path #5: LLL=0-6, MMMM=0-Eh, O=1 (2-byte match offset)
; Handle LLL=0-6 by jumping directly into # of bytes to copy (6 down to 1)
lit_len_mat_len_2b:
movsb
movsb
movsb
movsb
movsb
movsb
get_word_match_offset
copy_small_match_len
; Path #6: LLL=0-6, MMMM=Fh, O=1 (2-byte match offset)
lit_len_mat_ext_2b:
movsb
movsb
movsb
movsb
movsb
movsb
get_word_match_offset
copy_large_match_len
; Path #7: LLL=7, MMMM=0-Eh, O=1 (2-byte match offset)
lit_ext_mat_len_2b:
; on entry: ax=0 + token, bp=ax
lodsb ;grab extra literal length byte
add al,litrunlen ;add 7h literal run length
jz @@val249_7 ;if zf & cf, 249: get 16-bit literal length
jc @@val250_7 ;if cf, 250: get extra literal length byte
xchg cx,ax ;otherwise, we have our literal length
do_literal_copy ;this might be better as rep movsw !!! benchmark
get_word_match_offset
copy_small_match_len
@@val250_7:
lodsb ;ah=0; grab single extra length byte
inc ah ;ax=256+length byte
xchg cx,ax
do_literal_copy
get_word_match_offset
copy_small_match_len
@@val249_7:
lodsw ;grab 16-bit length
xchg cx,ax
do_literal_copy
get_word_match_offset
copy_small_match_len
; Path #8: LLL=7, MMMM=Fh, O=1 (2-byte match offset)
lit_ext_mat_ext_2b:
; on entry: ax=0 + token, bp=ax
lodsb ;grab extra literal length byte
add al,litrunlen ;add 7h literal run length
jz @@val249_8 ;if zf & cf, 249: get 16-bit literal length
jc @@val250_8 ;if cf, 250: get extra literal length byte
xchg cx,ax ;otherwise, we have our literal length
do_literal_copy ;this might be better as rep movsw !!! benchmark
get_word_match_offset
copy_large_match_len
@@val250_8:
lodsb ;ah=0; grab single extra length byte
inc ah ;ax=256+length byte
xchg cx,ax
do_literal_copy
get_word_match_offset
copy_large_match_len
@@val249_8:
lodsw ;grab 16-bit length
xchg cx,ax
do_literal_copy
get_word_match_offset
copy_large_match_len
done_decompressing:
;return # of decompressed bytes in ax
pop ax ;retrieve the original decompression offset
xchg di,ax ;compute decompressed size
sub ax,di
sub di,ax ;adjust for original offset
xchg di,ax ;return adjusted value in ax
ret ;done decompressing, exit to caller
;These are called less often; moved here to optimize the fall-through case
@@get_long_offset:
lodsw ;Get 2-byte match offset
jmp @@get_match_length
;With a confirmed longer match length, we have an opportunity to optimize for
;the case where a single byte is repeated long enough that we can benefit
;from rep movsw to perform the run (instead of rep movsb).
@@mid_matchlen:
lodsb ;grab single extra length byte
inc ah ;add 256
@@do_long_copy:
xchg cx,ax ;copy match length into cx
@@copy_len_preset:
push ds ;save ds
mov bp,es
mov ds,bp ;ds=es
mov bp,si ;save si
mov si,di ;ds:si now points at back reference in output data
add si,dx
cmp dx,-2 ;do we have a byte/word run to optimize?
jae @@do_run ;perform a run
;You may be tempted to change "jae" to "jge" because DX is a signed number.
;Don't! The total window is 64k, so if you treat this as a signed comparison,
;you will get incorrect results for offsets over 32K.
;If we're here, we have a long copy and it isn't byte-overlapping (if it
;overlapped, we'd be in @@do_run_1) So, let's copy faster with REP MOVSW.
;This won't affect 8088 that much, but it speeds up 8086 and higher.
shr cx,1
rep movsw
adc cx,0
rep movsb
mov si,bp ;restore si
pop ds
jmp @@decode_token ;go decode another token
@@do_run:
je @@do_run_2 ;fall through to byte (common) if not word run
@@do_run_1:
lodsb ;load first byte of run into al
mov ah,al
shr cx,1
rep stosw ;perform word run
adc cx,0
rep stosb ;finish word run
mov si,bp ;restore si
pop ds
jmp @@decode_token ;go decode another token
@@do_run_2:
lodsw ;load first word of run
shr cx,1
rep stosw ;perform word run
adc cx,0 ;despite 2-byte offset, compressor might
rep stosb ;output odd length. better safe than sorry.
mov si,bp ;restore si
pop ds
jmp @@decode_token ;go decode another token
ENDP lzsa1_decompress_speed_jumptable
ENDS CODE
@ -238,37 +513,11 @@ ENDS CODE
END
;Speed optimization history (decompression times in microseconds @ 4.77 MHz):
; original E. Marty code shuttle 123208 alice 65660 robotron 407338 ***
; table for shr al,4 shuttle 120964 alice 63230 robotron 394733 +++
; push/pop to mov/mov shuttle 118176 alice 61835 robotron 386762 +++
; movsw for literalcpys shuttle 124102 alice 64908 robotron 400220 --- rb
; stosw for byte runs shuttle 118897 alice 65040 robotron 403518 --- rb
; better stosw for runs shuttle 117712 alice 65040 robotron 403343 +--
; disable RLE by default shuttle 116924 alice 60783 robotron 381226 +++
; optimize got_matchlen shuttle 115294 alice 59588 robotron 374330 +++
; fall through to getML shuttle 113258 alice 59572 robotron 372004 +++
; fall through to midLI shuttle 113258 alice 59572 robotron 375060 ..- rb
; fall through midMaLen shuttle 113247 alice 59572 robotron 372004 +.+
; movsw for litlen > 255 shuttle 113247 alice 59572 robotron 371612 ..+
; rep stosw for long runs shuttle 113247 alice 59572 robotron 371612 ...
; rep movsw for long cpys shuttle 113247 alice 59572 robotron 371035 ..+
; xchg/dec ah -> mov ah,val shuttle 112575 alice 59272 robotron 369198 +++
; force >12h len.to longcpy shuttle 101998 alice 59266 robotron 364459 +.+
; more efficient run branch shuttle 102239 alice 59297 robotron 364716 --- rb
; even more eff. run branch shuttle 101998 alice 59266 robotron 364459 ***
; BUGFIX - bad sign compare shuttle 101955 alice 59225 robotron 364117 +++
; reverse 16-bit len compar shuttle 102000 alice 59263 robotron 364460 --- rb
; jcxz for EOD detection no change to speed, but is 1 byte shorter +++
; force movsw for literals shuttle 107183 alice 62555 robotron 379524 --- rb
; defer shr4 until necessry shuttle 102069 alice 60236 robotron 364096 ---
; skip literals if LLL=0 shuttle 98655 alice 57849 robotron 363358 ---
; fall through to mid_liter shuttle 98595 alice 57789 robotron 361998 +++
; == jumptable experiments begin ==
; jumptable for small copys shuttle 101594 alice 61078 robotron 386018 ---
; start:xchg instead of mov shuttle 100948 alice 60467 robotron 381112 +++
; use table for LLL=0 check shuttle 106972 alice 63333 robotron 388304 --- rb
; jmptbl to fallthrough mov shuttle 102532 alice 60760 robotron 383070 ---
; cpy fallthrough check_ofs shuttle 98939 alice 58917 robotron 371019 +**
; single jumptable jump shuttle 97528 alice 57264 robotron 362194 ++*
; conditional check for L=7 shuttle 98610 alice 58521 robotron 368153 --- rb
; defer add MIN_MATCH_SIZE shuttle 97207 alice 57200 robotron 362884 ++*
; jumptable rewrite, no RLE shuttle 97744 alice 46905 robotron 309032 -++
; adc cx,0 -> adc cl,0 shuttle 97744 alice 46893 robotron 309032 .+.!
; jumptable rewrite w/RLE shuttle 88776 alice 50433 robotron 319222 +--
; short match copies movsb shuttle 97298 alice 49769 robotron 326282 ---rb
; long match copy #1 16-bit shuttle 92490 alice 46905 robotron 308722 +*+
; long match copy #2 extraB shuttle 92464 alice 46905 robotron 308371 +.+
; long match copy #3 0f->ed shuttle 86765 alice 46864 robotron 303895 +++!