From: Al Viro Date: Wed, 18 Aug 2010 02:50:23 +0000 Subject: Re: [GIT] Sparc Message-Id: <20100818025022.GM31363@ZenIV.linux.org.uk> List-Id: References: <20100817.180325.104051399.davem@davemloft.net> <20100817.191245.112612004.davem@davemloft.net> In-Reply-To: <20100817.191245.112612004.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Miller Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org On Tue, Aug 17, 2010 at 07:12:45PM -0700, David Miller wrote: > From: Linus Torvalds > 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.