如何将两个32位寄存器移至一个64位寄存器？
假设我想将两个 32 位寄存器 EAX 作为低 32 位字，将 EDX 作为高 32 位字放入 RAX 中。 我找到了一种方法：
shl rdx, 32
or rax, rdx
只有当我们确定RAX的32到61位为0时，此方法才有效。如果我们不确定这一点，那么我们必须首先清除高32位字，比如：
mov eax, eax //This instruction should clear the high 32 bit word of RAX
这是最短路线吗？
是否有单个 asm x86-64 指令执行此操作？
Let's say that I want to put two 32 bit registers EAX as low 32 bit word and EDX as high 32 bit word into RAX.
I have found one way:
shl rdx, 32
or rax, rdx
This method works only if we are sure that bits from 32 to 61 of RAX are 0. If we are not sure about that, then we must first clear the high 32 bit word, like:
mov eax, eax //This instruction should clear the high 32 bit word of RAX
Is this the shortest way?
Is there a single asm x86-64 instruction that does this operation?
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也许这更好一点：
不假设高双字为零。
Perhaps this is a tad better:
Does not assume that high dwords are zero.