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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 xchg cx,ax
rep movsb ; copy cx literals from ds:si to es:di 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 js .rep_match_or_large_offset
cmp dl,040H ; check if this is a 5 or 9-bit offset (Y bit) ;;cmp dl,040H ; check if this is a 5 or 9-bit offset (Y bit)
jnb .offset_9_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 ; 5 bit offset
xchg cx,ax ; clear ah - cx is zero from the rep movsb above cmp dl,020H ; test bit 5
mov al,020H ; shift Z (offset bit 4) in place call .get_nibble_x
and al,dl jmp short .dec_offset_top
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
.offset_9_bit: ; 9 bit offset .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 lodsb ; get 8 bit offset from stream in A
dec ah ; set offset bits 15-8 to 1 dec ah ; set offset bits 15-8 to 1
test dl,020H ; test bit Z (offset bit 8) test dl,020H ; test bit Z (offset bit 8)
je .get_match_length je .get_match_length
.dec_offset_top:
dec ah ; clear bit 8 if Z bit is clear dec ah ; clear bit 8 if Z bit is clear
; or set offset bits 15-8 to 1
jmp short .get_match_length jmp short .get_match_length
.rep_match_or_large_offset: .rep_match_or_large_offset:
@ -99,25 +94,22 @@ lzsa2_decompress:
; 13 bit offset ; 13 bit offset
mov ah,020H ; shift Z (offset bit 12) in place cmp dl,0A0H ; test bit 5 (knowing that bit 7 is also set)
and ah,dl xchg ah,al
shl ah,1 call .get_nibble_x
shl ah,1 sub al,2 ; substract 512
call .get_nibble ; get nibble for offset bits 8-11 jmp short .get_match_length_1
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
.rep_match_or_16_bit: .rep_match_or_16_bit:
test dl,020H ; test bit Z (offset bit 8) test dl,020H ; test bit Z (offset bit 8)
jne .repeat_match ; rep-match jne .repeat_match ; rep-match
; 16 bit offset ; 16 bit offset
lodsw ; Get 2-byte match offset lodsb ; Get 2-byte match offset
.get_match_length_1:
xchg ah,al xchg ah,al
lodsb ; load match offset bits 0-7
.get_match_length: .get_match_length:
xchg bp,ax ; bp: offset xchg bp,ax ; bp: offset
@ -147,8 +139,7 @@ lzsa2_decompress:
xchg si,ax xchg si,ax
push es push es
pop ds pop ds
mov si,di ; ds:si now points at back reference in output data lea si,[bp+di] ; ds:si now points at back reference in output data
add si,bp
rep movsb ; copy match rep movsb ; copy match
xchg si,ax ; restore ds:si xchg si,ax ; restore ds:si
pop ds pop ds
@ -160,6 +151,15 @@ lzsa2_decompress:
sub ax,di sub ax,di
ret ; done 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: .get_nibble:
neg bh ; nibble ready? neg bh ; nibble ready?
jns .has_nibble jns .has_nibble