pic乘除运算子程序

#define STATUS 3

#define skpb skpnc ;skip if borrowed
#define skpnb skpc ;skip if no borrow

cblock 0x10
PROD:2 ;2 bytes for production
QUOT:2 ;2 bytes for quotient
PAVRA ;divider/multiplier
PAVRB ;reminder / multiplier
PAVRC ;additional byte space
mcount ;loop counter
endc

org 000h

;movlw 0x20;
;movwf PAVRA
;movlw 0x30
;movwf PAVRB

call BBYTE_DIV

goto $-1

;====================================
;PROD:2 = PAVRA * PAVRB
;====================================
BYTE_MUL
clrf PROD
clrf PROD+1
movlw .8
movwf mcount
_mul1
rlf PROD,f ;left shift 16-bit with LSB=0
bcf PROD,0
rlf PROD+1,f
rlf PAVRA,w ;make left-rotate shift
rlf PAVRA,f ;and check MSB
skpc ;skip if MSB=1
goto _mul2 ;MSB=0
;do when MSB=1
movf PAVRB,w
addwf PROD,f
skpnc
incf PROD+1,f
_mul2
decfsz mcount,f
goto _mul1
retlw 0


;====================================
;WORD divided by BYTE =
;PROD:2 / PAVRA =
;QUOT:2 = Quotient =
;PAVRB = Reminder =
;====================================
WBYTE_DIV
movf PAVRA,f
skpnz
retlw 1 ;return if divider=0
clrf PAVRB
clrf PAVRC
clrf QUOT
clrf QUOT+1
movlw .16
movwf mcount
_wdiv1
rlf QUOT,f ;adjust Quotient
rlf QUOT+1,f
bcf QUOT,0
;
rlf PROD+1,w
rlf PROD,f
rlf PROD+1,f
;
rlf PAVRB,f
rlf PAVRC,f
;
movf PAVRA,w
subwf PAVRB,f
skpb ;skip if borrow
goto _wdiv2
;if borrow
btfsc PAVRC,0
goto _wdiv2
addwf PAVRB,f
bcf PAVRC,0
goto _wdiv3
_wdiv2 ;if no borrow
bcf PAVRC,0
bsf QUOT,0
_wdiv3
decfsz mcount,f
goto _wdiv1
retlw 0

;====================================
;BYTE divided by BYTE =
;PROD[0] / PAVRA =
;QUOT[0] = Quotient =
;PAVRB = Reminder =
;====================================
BBYTE_DIV
movf PAVRA,f
skpnz
retlw 1 ;return if divider=0
clrf PAVRB ;clear reminder
clrf QUOT ;clear quotient
movlw .8
movwf mcount ;for 8 times shift
_bdiv1
rlf QUOT,f ;adjust Quotient
bcf QUOT,0 ;left shift i bit
;
rlf PROD,w ;get 1 bit, MSB first
rlf PROD,f ;do rotate shift
;
rlf PAVRB,f ;set to LSB of reminder
;
movf PAVRA,w ;reminder - divider
subwf PAVRB,f
skpb ;skip if borrow
goto _bdiv2
;do if borrowed
addwf PAVRB,f ;cancel subtraction
goto _bdiv3 ;go for next
_bdiv2 ;do if no borrow
bsf QUOT,0 ;reminder > divider
;update quotient
_bdiv3
decfsz mcount,f ;loop test
goto _bdiv1 ;do 8 times
retlw 0 ;completed

END

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