Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760589Ab2EWQ6M (ORCPT ); Wed, 23 May 2012 12:58:12 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:45948 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751145Ab2EWQ6K (ORCPT ); Wed, 23 May 2012 12:58:10 -0400 MIME-Version: 1.0 In-Reply-To: <20120523165303.GB18284@liondog.tnic> References: <1337684026-19740-1-git-send-email-bp@amd64.org> <1337789429.9783.16.camel@laptop> <4FBD0C47.70600@zytor.com> <20120523161932.GN14757@aftab.osrc.amd.com> <1337790571.9783.28.camel@laptop> <4FBD10D5.6080602@zytor.com> <20120523165303.GB18284@liondog.tnic> From: Linus Torvalds Date: Wed, 23 May 2012 09:57:47 -0700 X-Google-Sender-Auth: -ktiQsvFB-o-3Mz5F_4QaJKQ0uM Message-ID: Subject: Re: [tip:x86/mce] x86/bitops: Move BIT_64() for a wider use To: Borislav Petkov , "H. Peter Anvin" , Peter Zijlstra , Borislav Petkov , mingo@kernel.org, linux-kernel@vger.kernel.org, frank.arnold@amd.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1047 Lines: 29 On Wed, May 23, 2012 at 9:53 AM, Borislav Petkov wrote: > > How about the following completely untested chunk: No, you can't do that. All standard C operations will return *one* type. That very much includes the ternary ?: operator. The *only* ways I know of to get two types are - C preprocessor stuff, ie #define BIT(x) __BIT_##x and then just enumerate all the 64 cases. This is portable, but it gets old. - using __builtin_choose_expr(), which actually allows the two expressions to have different types, but requires a very strict compile-time constant (ie you cannot rely on the optimizer making it a constant - because it needs to choose the expression before the optimizer runs) There might be some other magic gcc extension, of course. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/