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a bit faster, a bit smaller

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This commit is contained in:
Peter Ferrie 2019-07-03 19:38:27 -07:00
parent da4f6f7882
commit 32b98f3085
2 changed files with 21 additions and 20 deletions
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29
asm/8088/decompress_small_v1.S
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@ -54,11 +54,12 @@ lzsa1_decompress:
jne .mid_literals
lodsw ; grab 16-bit extra length
jmp short .got_literals
.byte 81H ; mask inc ah/lodsb
; (*like jmp short .got_literals but faster)
.mid_literals:
lodsb ; grab single extra length byte
inc ah ; add 256
lodsb ; grab single extra length byte
.got_literals:
xchg cx,ax
@ -67,16 +68,17 @@ lzsa1_decompress:
test dl,dl ; check match offset size in token (O bit)
js .get_long_offset
xchg ax,cx ; clear ah - cx is zero from the rep movsb above
dec cx
xchg cx,ax ; ah to 0xff - cx was zero from the rep movsb above
lodsb
dec ah
jmp short .get_match_length
.byte 3CH ; mask lodsw
; (*like jmp short .get_match_length but faster)
.get_long_offset:
lodsw ; Get 2-byte match offset
.get_match_length:
xchg ax,dx ; dx: match offset ax: original token
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
@ -90,8 +92,13 @@ lzsa1_decompress:
lodsw ; grab 16-bit length
test ax,ax ; bail if we hit EOD
je short .done_decompressing
jmp short .got_matchlen
jne short .got_matchlen
.done_decompressing:
pop ax ; retrieve the original decompression offset
xchg ax,di ; compute decompressed size
sub ax,di
ret ; done
.mid_matchlen:
lodsb ; grab single extra length byte
@ -109,9 +116,3 @@ lzsa1_decompress:
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

12
asm/8088/decompress_small_v2.S
View File

@ -72,7 +72,7 @@ lzsa2_decompress:
jnb .offset_9_bit
; 5 bit offset
xchg ax,cx ; clear ah - cx is zero from the rep movsb above
xchg cx,ax ; clear ah - cx is zero from the rep movsb above
mov al,020H ; shift Z (offset bit 4) in place
and al,dl
shl al,1
@ -85,7 +85,7 @@ lzsa2_decompress:
jmp short .get_match_length
.offset_9_bit: ; 9 bit offset
xchg ax,cx ; clear ah - cx is zero from the rep movsb above
xchg cx,ax ; clear ah - cx is zero from the rep movsb above
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)
@ -120,9 +120,9 @@ lzsa2_decompress:
xchg ah,al
.get_match_length:
mov bp,ax ; bp: offset
xchg bp,ax ; bp: offset
.repeat_match:
mov ax,dx ; ax: original token
xchg ax,dx ; ax: original token
and al,07H ; isolate match length in token (MMM)
add al,2 ; add MIN_MATCH_SIZE_V2
@ -156,7 +156,7 @@ lzsa2_decompress:
.done_decompressing:
pop ax ; retrieve the original decompression offset
xchg ax,di ; compute decompressed size
xchg di,ax ; compute decompressed size
sub ax,di
ret ; done
@ -166,7 +166,7 @@ lzsa2_decompress:
xchg bx,ax
lodsb ; load two nibbles
xchg ax,bx
xchg bx,ax
.has_nibble:
mov cl,4 ; swap 4 high and low bits of nibble