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This commit is contained in:
Peter Ferrie 2019-07-09 16:49:01 -07:00
parent 467cd1970f
commit e85cb8a5bb
1 changed files with 21 additions and 22 deletions
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43
asm/8088/decompress_small_v2.S
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@ -65,27 +65,21 @@ lzsa2_decompress:
xchg cx,ax
rep movsb ; copy cx literals from ds:si to es:di
test dl,dl ; check match offset mode in token (X bit)
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)
jnb .offset_9_bit
;;cmp dl,040H ; check if this is a 5 or 9-bit offset (Y bit)
; discovered via the test with bit 6 set
xchg cx,ax ; clear ah - cx is zero from the rep movsb above
jne .offset_9_bit
; 5 bit offset
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
shl 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
cmp dl,020H ; test bit 5
call .get_nibble_x
dec ah ; set offset bits 15-8 to 1
jmp short .get_match_length
.offset_9_bit: ; 9 bit offset
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)
@ -99,15 +93,11 @@ lzsa2_decompress:
; 13 bit offset
mov ah,020H ; shift Z (offset bit 12) in place
and ah,dl
shl ah,1
shl ah,1
call .get_nibble ; get nibble for offset bits 8-11
or ah,cl ; merge nibble
rol ah,1
xor ah,0E1H ; set offset bits 15-13 to 1
sub ah,2 ; substract 512
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
xchg ah,al
lodsb ; load match offset bits 0-7
jmp short .get_match_length
@ -160,6 +150,15 @@ lzsa2_decompress:
sub ax,di
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