From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756328AbaEaQPd (ORCPT ); Sat, 31 May 2014 12:15:33 -0400 Received: from mail-ie0-f170.google.com ([209.85.223.170]:39079 "EHLO mail-ie0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752661AbaEaQPb (ORCPT ); Sat, 31 May 2014 12:15:31 -0400 MIME-Version: 1.0 In-Reply-To: <5507335.AOOTyGEum3@wuerfel> References: <1401480116-1973111-1-git-send-email-arnd@arndb.de> <5507335.AOOTyGEum3@wuerfel> Date: Sat, 31 May 2014 18:15:30 +0200 X-Google-Sender-Auth: oqNKIEU8z-wttahMSI4C4egPkB0 Message-ID: Subject: Re: [RFC 01/32] fs: introduce new 'struct inode_time' From: Geert Uytterhoeven To: Arnd Bergmann Cc: Andreas Schwab , "linux-kernel@vger.kernel.org" , Linux-Arch , "Joseph S. Myers" , John Stultz , Christoph Hellwig , Thomas Gleixner , Ley Foon Tan , "H. Peter Anvin" , Linux FS Devel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 31, 2014 at 4:54 PM, Arnd Bergmann wrote: > On Saturday 31 May 2014 10:39:02 Andreas Schwab wrote: >> Geert Uytterhoeven writes: >> >> > Hi Arnd, >> > >> > On Fri, May 30, 2014 at 10:01 PM, Arnd Bergmann wrote: >> >> + * The variant using bit fields is less efficient to access, but >> >> + * small and has a wider range as the 32-bit one, plus it keeps >> >> + * the signedness of the original timespec. >> >> + */ >> >> +struct inode_time { >> >> + long long tv_sec : 34; >> >> + int tv_nsec : 30; >> >> +}; >> > >> > Don't you need 31 bits for tv_nsec, to accommodate for the sign bit? >> > I know you won't really store negative numbers there, but storing a large >> > positive number will become negative on read out, won't it? >> >> Only if the int bitfield is signed. Bitfields are weird, aren't they? According to 6.7.2#5 (thanks for the reference), this is implementation defined. > It was a mistake on my side, as I didn't know about that rule and > meant write 'unsigned int' really. Also, I always have a bad feeling IC, but the comment said "plus it keeps the signedness". So it doesn't keep the signedness for the tv_nsec field. > about using bitfields in general. Hehe... Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds