汇编语言:cbw [英] Assembly Language: cbw

问题描述

我不确定cbw命令的实际作用.我有一段代码:

I am unsure of what the cbw command actually does. I have a snippet of code:

mov  ax,0FF0h
cbw
idiv ah

cbw之后ax的值如何变化?

How does the value of ax change after cbw?

推荐答案

cbw指令将一个字节扩展为一个单词.在这种情况下，它将使用AL的符号位(恰好是1)并将其复制到AH的每一位.

The cbw instruction sign-extends a byte into a word. In this case, it'll take the sign bit of AL (which happens to be 1) and copy it into every bit of AH.

这意味着AX的二进制补码值将相同，但是二进制表示形式将不同.

This means that the two's-complement value of AX will be the same, but the binary representation will be different.

cbw指令后的AX值将为FFF0h(16位-16值，就像AL最初是8位-16一样)

The value of AX after the cbw instruction will be FFF0h (a 16-bit -16 value, just like AL was originally an 8-bit -16)

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