Re: [patch 2.6.13-rc3] i386: clean up user_mode macros

[Linus Torvalds <torvalds@osdl.org>]

On Mon, 25 Jul 2005, Chuck Ebbert wrote:
> 
> Recent patches from the Xen group changed the X86 user_mode macros.
> 
> This patch does the following:
> 
>         1. Makes the new user_mode() return 0 or 1 (same as x86_64)

I _really_ prefer

	x != 0

over 

	!!x

since double negation is not only a bad habit in natural languages, it's a 
bad habit in computer languages too, for exactly the same reason. It's 
confusing.

Ask a hundred random C programmers what "!!x" means, versus what "x != 0"
means, and time their replies.

I will bet you $5 USD that even if they all give the right answer (and I
suspect you'll get a few wrogn answers in there too for the !! case),
they'll take a _lot_ longer answering the "!!x" version than they will the 
"x != 0" question.

And guess what? That means that the "!!x" version is worse. It means that
people don't "see" what it means - they have to think about it. And you
shouldn't have to think about something like that, you should write it in 
the obvious way in the first place.

		Linus
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