Assembly language (7) operation instruction

1 mul ride

assume cs:code

code segment

main proc
	mov ax,5
	mov bx,2
	mul bx
	MOV AX,4C00H
	INT	21H
main endp
start:call main
code ends
end start

mul Write a register after , Another automatic call ax, The results are stored in ax in , If it is greater than 16 Bits exist DX：AX in .

2 div except

assume cs:code

code segment

main proc
	mov ax,5
	mov bx,2
	div bx
	MOV AX,4C00H
	INT	21H
main endp
start:call main
code ends
end start

ax Storage providers ,dx Store the remainder .

3 An operation

xor Exclusive or Two operands , Put it in the first operand
and And Two operands , Put it in the first operand
or or Two operands , Put it in the first operand
not Take the opposite An operand

4 Shift instructions

​ There are many shift commands in assembly , Shift left and shift right have different types .

Move left
​ Left shift yes SHL（ Logic shift left ）、SAL（ Arithmetic shift left ） , Both are shifted to the left , All use 0 To fill the empty bits generated by the shift . There is no difference between the two .

​ Move left and ROL（ Cyclic shift to the left ）、RCL（ Shift left with carry cycle ）, Cyclic shift to the left , As the name suggests, it circulates to the left ; Loop with carry shifts left , That is, the result of the shift “ overflow ” Bit shift in CF in , primary CF The value in moves into the number .

Move right
​ Shift right yes SHR（ Logical shift right ）、SAR（ Arithmetic shift right ）, The positions resulting from arithmetic shift right are filled with sign bits ; Logical shift right use 0 fill .

​ Move right and ROR（ Cycle moves to the right ）、RCR（ Shift right with carry cycle ）, Similar to left shift loop and carry loop .