From owner-sc22wg5+sc22wg5-dom8=www.open-std.org@open-std.org Thu Jan 17 17:09:56 2013 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id A2188356A27; Thu, 17 Jan 2013 17:09:31 +0100 (CET) Delivered-To: sc22wg5@open-std.org Received: from exprod6og114.obsmtp.com (exprod6og114.obsmtp.com [64.18.1.33]) by www.open-std.org (Postfix) with ESMTP id 9535B356957 for ; Thu, 17 Jan 2013 17:09:12 +0100 (CET) Received: from CFWEX01.americas.cray.com ([136.162.34.11]) (using TLSv1) by exprod6ob114.postini.com ([64.18.5.12]) with SMTP ID DSNKUPgGXwnPscAt8A9EhGe9Modmd8V9g3NA@postini.com; Thu, 17 Jan 2013 06:10:51 PST Received: from fortran.us.cray.com (172.31.19.200) by CFWEX01.americas.cray.com (172.30.88.25) with Microsoft SMTP Server id 14.2.318.1; Thu, 17 Jan 2013 08:06:39 -0600 Message-ID: <50F80574.4020402@cray.com> Date: Thu, 17 Jan 2013 08:06:44 -0600 From: Bill Long Reply-To: Organization: Cray Inc. User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: sc22wg5 Subject: Re: (j3.2006) (SC22WG5.4904) [ukfortran] Comment on a comment on the WG5 letterballot on N1947 References: <20130108205438.50F4E356B56@www.open-std.org><20130113210632.B1C67356BEA@www.open-std.org><20130116050422.92E30356BE0@www.open-std.org><20130116191114.A6A75356A2B@www.open-std.org><20130116223411.D135F356A2B@www.open-std.org> <20130116231527.45C11356C30@www.open-std.org> <20130117025541.22E48356C9E@www.open-std.org> In-Reply-To: <20130117025541.22E48356C9E@www.open-std.org> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-sc22wg5@open-std.org Precedence: bulk On 1/16/13 6:57 PM, Malcolm Cohen wrote: >> Of course, there are numerous cases, almost all related to user-written random >> number generators, where overflow of integer multiply is intentional. > > (0) Random number generators have also been available on machines with hardware > always-on integer overflow detection. > Yes, I remember this from the VAX era. > (1) This is almost certainly entirely unnecessary. Many good generators don't > need this. > I said the practice was "intentional", not necessary. Indeed, such generators tend to be of poorer quality, though they are very fast. > (2) It is not exactly beyond the wit of man to avoid using a compiler option > when it is undesired! VAX users quickly learned that. But irrelevant to the point that the integer overflow was intentional, and not an error that needed to be exposed. > >> For Fortran, and a program with arrays this large, users would instinctively >> set a compiler switch to make 64-bit integers the default. > > Ah yes, the "non-Fortran" switch (unless it also doubles the sizes of default > real and double precision). > Indeed. I much prefer a "default64" switch that does both integer and real, as opposed to the independent-r8 / -i8 style switches. It would be even better for the programmer to not use default integer or real declarations, but include specific KIND parameters. Unfortunately it is hard to change old habits. As an example, the brand new MPI 3 Fortran interface still uses default INTEGER declarations. Cheers, Bill -- Bill Long longb@cray.com Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101