Using AND instruction with 32-bit operand in 64-bit

0

I have a question on the AND instruction in 64-bit mode. I have this manual telling me that the AND 32-bit immediate is to be sign-extended to 64-bit. But I can't do this

and rax,0x80000000

Which is ridiculous I think because 0x800000 is a perfect DWORD operand. The highest I can go with it is

and rax,0x7fffffff

So what's happening here? I can't use MSb=1 to sign-extend an operand? If so, then how's sign-extension is supposed to work against an operand without being able to use it as in 0x80000000?

Thanks for you replies.

assembly
x86
size
x86-64
operands
asked on Stack Overflow Nov 19, 2018 by royalfinest

1 Answer

-1

“by preventing people from doing something stupid, you might prevent them from doing something clever”: an attitude born of respect and humility; you don’t know all the answers, so don’t impose random stupidity like Jester pointed out in the comments.

fwiw, gcc / gnu as understands:

and $0x80000000, %rax

clang, religiously infused, insisted upon:

and $0xffffffff80000000, %rax

now, quick, are there enough f’s there? Does this help readability? If you don’t understand sign extension, how much assembly are you going to understand anyways?

answered on Stack Overflow Nov 22, 2018 by mevets

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