MASM-两个16位二进制数减法模拟

al,[bx][si]
        cmp al,''''0''''
        jz  qb1
        mov al,''''0''''
        mov [bx][si],al
        jmp qb2
qb1:
        mov al,''''1''''
        mov [bx][si],al
qb2:
        inc si
        cmp si,16
        jl  qbroat

qnext:     
        mov dh,1      ;加1处理.方法类似减法
        mov si,15
qbincre:
        mov al,[bx][si]
        sub al,''''0''''
        add al,dh
        mov dh,0

        cmp al,2
        jnz qbi1
        mov al,0
        mov dh,1
qbi1:
        add al,''''0''''
        mov [bx][si],al
        dec si
        cmp si,0
        jnl qbincre
qbret:
        ret
questBuma endp

;*******************************************
bsubproc proc near   ;功能:16位二进制数减法模拟.
     ;算法:逐位相减,flag为借位标志(BX)
        push ax
        push bx
        push cx
        push si

        mov bx,0 ;//flag
        mov si,15

broat:  mov al,num1[si]
        add al,bh
        mov bh,0   ;//clear bh
        cmp al,num2[si]
        jnl bnext
        add al,2
        dec bh
bnext:  
        sub al,num2[si]
        add al,''''0''''
        mov sum[si],al
        dec si
        cmp si,0
        jnl  broat  &