linux nasm move a value in AL up to AX

问题

I am working on a way to print multiple digit integers by dividing the integer by 10 repeatedly and collecting the remainders, then printing them. Here is a code segment that has the problem:

Divide:

    ; initial division
    mov ax, 111   ; number we want to print
    mov ch, 10    ; we divide by ten to siphon digits
    div ch        ; divide our number by 10

    ; al now has 11, ah has 1
    mov dh, ah ; save the remainder in dh
  1 mov bx, al ; these lines refill ax with the number to 
    mov ax, bx ; divide
    mov ch, 10 ; refill ch with the divisor
    div ch     ; al now has 1, ah now has 1

The line marked with 1 has the problem. I need to move a value in 8 bit register AL to a 16 bit register AX. How can I get that value there so I can divide it?

回答1:

Just clear the ah register instead. The ax register consists of it's high and low part - ah:al

The same applies to bx (bh,bl) cx (ch,cl) and dx (dh,dl) registers

来源：https://stackoverflow.com/questions/12879740/linux-nasm-move-a-value-in-al-up-to-ax