Thuat toan chia

[falleaf]

#define bf_carry 3, 0
#define bf_zero 3, 2

#define same 1
#define wreg 0

#define stc bsf bf_carry
#define clc bcf bf_carry

;-[ Div ]--------------------------------------------------------------
; Call w/: Number in f_divhi:f_divlo, divisor in W.
; Returns: Quotient in f_divlo, remainder in f_divhi. W preserved.
;          Carry set if error. Z if divide by zero, NZ if divide overflow.
; Notes:   Works by left shifted subtraction.
;          Size = 29, Speed(w/ call&ret) = 7 cycles if div by zero
;          Speed = 94 minimum, 129 maximum cycles

Div;
    addlw 0          ; w+=0 (to test for div by zero)
    stc              ; set carry in case of error
    btfsc bf_zero    ; if zero
     return          ;   return (error C,Z)

    call DivSkipHiShift
iDivRepeat = 8
while iDivRepeat

    call DivCode

iDivRepeat--
endw

    rlf f_divlo, same ; C << lo << C

    ; If the first subtract didn't underflow, and the carry was shifted
    ; into the quotient, then it will be shifted back off the end by this
    ; last RLF. This will automatically raise carry to indicate an error.
    ; The divide will be accurate to quotients of 9-bits, but past that
    ; the quotient and remainder will be bogus and carry will be set.

    bcf bf_zero  ; NZ (in case of overflow error)
    return       ; we are done!

DivCode
    rlf f_divlo, same    ; C << lo << C
    rlf f_divhi, same    ; C << hi << C
    btfss bf_carry       ; if Carry
     goto DivSkipHiShift ;
    subwf f_divhi, same  ;   hi-=w
    stc                  ;   ignore carry
    return               ;   done
                         ; endif
DivSkipHiShift
    subwf f_divhi, same  ; hi-=w
    btfsc bf_carry       ; if carry set
     return              ;   done
    addwf f_divhi, same  ; hi+=w
    clc                  ; clear carry
    return               ; done

Đây là thuật toán chia 16bit cho 8bit. Bạn tìm hiểu và phân tích thêm nhé, có lẽ mafd_47a sẽ giúp bạn phân tích source code này thêm.

Chúc vui.

[anhquangngai]

Nguyên văn bởi falleaf

#define bf_carry 3, 0
#define bf_zero 3, 2

#define same 1
#define wreg 0

#define stc bsf bf_carry
#define clc bcf bf_carry

;-[ Div ]--------------------------------------------------------------
; Call w/: Number in f_divhi:f_divlo, divisor in W.
; Returns: Quotient in f_divlo, remainder in f_divhi. W preserved.
;          Carry set if error. Z if divide by zero, NZ if divide overflow.
; Notes:   Works by left shifted subtraction.
;          Size = 29, Speed(w/ call&ret) = 7 cycles if div by zero
;          Speed = 94 minimum, 129 maximum cycles

Div;
    addlw 0          ; w+=0 (to test for div by zero)
    stc              ; set carry in case of error
    btfsc bf_zero    ; if zero
     return          ;   return (error C,Z)

    call DivSkipHiShift
iDivRepeat = 8
while iDivRepeat

    call DivCode

iDivRepeat--
endw

    rlf f_divlo, same ; C << lo << C

    ; If the first subtract didn't underflow, and the carry was shifted
    ; into the quotient, then it will be shifted back off the end by this
    ; last RLF. This will automatically raise carry to indicate an error.
    ; The divide will be accurate to quotients of 9-bits, but past that
    ; the quotient and remainder will be bogus and carry will be set.

    bcf bf_zero  ; NZ (in case of overflow error)
    return       ; we are done!

DivCode
    rlf f_divlo, same    ; C << lo << C
    rlf f_divhi, same    ; C << hi << C
    btfss bf_carry       ; if Carry
     goto DivSkipHiShift ;
    subwf f_divhi, same  ;   hi-=w
    stc                  ;   ignore carry
    return               ;   done
                         ; endif
DivSkipHiShift
    subwf f_divhi, same  ; hi-=w
    btfsc bf_carry       ; if carry set
     return              ;   done
    addwf f_divhi, same  ; hi+=w
    clc                  ; clear carry
    return               ; done

Đây là thuật toán chia 16bit cho 8bit. Bạn tìm hiểu và phân tích thêm nhé, có lẽ mafd_47a sẽ giúp bạn phân tích source code này thêm.

Chúc vui.

vậy thì khi muốn chia thì làm như thế nào?
Anh có thể chỉ cụ thể hơn dc ko?