如何将两个寄存器的mul结果存储到内存中 [英] How to store a two-register mul result into memory

问题描述

所以，假设我在dx:ax中得到了mul的结果，如何将其保存到dword [ebx]?

So let's say that I've got a result of mul in dx:ax, how can I save it to dword [ebx]??

我对双字有同样的问题:edx(上半部分)和eax(下半部分)指向[ebx]所指向的两个dword.

I have the same problem with double words : edx (high half) and eax (low half) to two dwords pointed to by [ebx].

推荐答案

正如评论员Michael和Ped7g所说，您已经使用了偏移量.让我解释一下:

As said by commenters Michael and Ped7g already, you have use offsets. Let me explain:

x86以little-endian格式存储数字，这意味着最低顺序的字节首先存储在内存中.一个小例子:假设您在eax中具有值0x12345678，并执行以下指令:

x86 stores numbers in little-endian format, meaning that the lowest-order bytes are stored first in memory. A little example: Assuming you have the value 0x12345678 in eax, and you execute this instruction:

mov [addr], eax

...然后，地址addr上的内存将如下所示:

...then the memory at address addr will look like this:

78 56 34 12

在您的示例中，您在dx:ax中有一个值，它是在dx中具有值的高16位，在ax中具有值的低16位"的简写.再次假设该值是0x12345678，因此在dx中具有0x1234，在ax中具有0x5678，则需要两个移动指令:

In your example, you have a value in dx:ax which is a shorthand for "have a value's upper 16 bits in dx and its lower 16 bits in ax". Assuming the value is, again, 0x12345678, so you have 0x1234 in dx and 0x5678 in ax, then you need two move instructions:

mov [addr], ax   // Memory now looks like this: 78 56
mov [addr+2], dx // Memory now looks like this: 78 56 34 12

+2来自以下事实:ax是一个16位寄存器，即，它存储在内存中时会占用两个字节，因此，由于要在其后放置dx，因此需要增加地址是2.

The +2 comes from the fact that ax is a 16-bit register, i.e. it uses up two bytes when stored in memory, so since you want to put dx right after it, you need to increase the address by 2.

与edx和eax中的64位值(偏移量为4)相同.假设您将值0x1234567890ABCDEF拆分为edx中的0x12345678和eax中的0x90ABCDEF，那么它看起来像这样:

Same thing for 64-bit values in edx and eax, with an offset 4. Let's assume you have the value 0x1234567890ABCDEF split to 0x12345678 in edx and 0x90ABCDEF in eax, then it would look like this:

mov [addr], eax   // Memory now looks like this: EF CD AB 90
mov [addr+4], edx // Memory now looks like this: EF CD AB 90 78 56 34 12

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