linux-kernel - Re: [GIT] Sparc

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Message-ID: <20100818025022.GM31363@ZenIV.linux.org.uk>
Date:	Wed, 18 Aug 2010 03:50:23 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT] Sparc

On Tue, Aug 17, 2010 at 07:12:45PM -0700, David Miller wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Tue, 17 Aug 2010 18:31:50 -0700
> 
> > Confused yet?
> 
> Beyond...
> 
> > The basic rule becomes: never _ever_ overflow 'int' in a constant,
> > without specifying the exact type you want. That way you avoid all the
> > subtle cases.
> 
> That's easier to understand.

Actually, it's not that complicated:

1) base and suffices choose the possible types.
2) order of types is always the same: int -> unsigned -> long -> unsigned
long -> long long -> unsigned long long
3) we always choose the first type the value would fit into
4) L in suffix == "at least long"
5) LL in suffix == "at least long long"
6) U in suffix == "unsigned"
7) without U in suffix, base 10 == "signed"

That's it.  C90 differs from C99 only in one thing - long long (and LL) isn't
there.  The subtle mess Linus has mentioned is C90 gccism: gcc has allowed
unsigned long for decimal constants, as the last resort.  I.e. if you had
a plain decimal constant that wouldn't fit into long but would fit into
unsigned long, gcc generated a warning and treated it as unsigned long.
C90 would reject the damn thing.  _Bad_ extension, since in C99 the same
constant would be a legitimate signed long long.

But yes, "use the suffix when unsure" is a damn good idea, _especially_ since
the sizeof(long) actually varies between the targets we care about.
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