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Merge pull request #10 from peterferrie/master - 17 bytes smaller

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smaller
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Emmanuel Marty 2019-07-10 11:36:00 +02:00 committed by GitHub
commit f52ba3c40c
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1 changed files with 29 additions and 29 deletions
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58
asm/8088/decompress_small_v2.S
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@ -65,32 +65,27 @@ 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
dec ah ; set offset bits 15-8 to 1
jmp short .get_match_length
cmp dl,020H ; test bit 5
call .get_nibble_x
jmp short .dec_offset_top
.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)
je .get_match_length
.dec_offset_top:
dec ah ; clear bit 8 if Z bit is clear
; or set offset bits 15-8 to 1
jmp short .get_match_length
.rep_match_or_large_offset:
@ -99,25 +94,22 @@ 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
lodsb ; load match offset bits 0-7
jmp short .get_match_length
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
jmp short .get_match_length_1
.rep_match_or_16_bit:
test dl,020H ; test bit Z (offset bit 8)
jne .repeat_match ; rep-match
; 16 bit offset
lodsw ; Get 2-byte match offset
lodsb ; Get 2-byte match offset
.get_match_length_1:
xchg ah,al
lodsb ; load match offset bits 0-7
.get_match_length:
xchg bp,ax ; bp: offset
@ -147,8 +139,7 @@ lzsa2_decompress:
xchg si,ax
push es
pop ds
mov si,di ; ds:si now points at back reference in output data
add si,bp
lea si,[bp+di] ; ds:si now points at back reference in output data
rep movsb ; copy match
xchg si,ax ; restore ds:si
pop ds
@ -160,6 +151,15 @@ 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