Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.glorb.com!usenet.stanford.edu!not-for-mail From: Ben Pfaff Newsgroups: comp.programming Subject: Re: 64 bit code Date: Fri, 12 Oct 2012 20:07:11 -0700 Lines: 18 Message-ID: <871uh36peo.fsf@blp.benpfaff.org> References: <507595db$0$6898$e4fe514c@news2.news.xs4all.nl> <162dnU-Rw5IpVOrNnZ2dnUVZ8qCdnZ2d@bt.com> Reply-To: blp@cs.stanford.edu Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: usenet.stanford.edu 1350097632 21480 127.0.0.1 (13 Oct 2012 03:07:12 GMT) X-Complaints-To: action@cs.stanford.edu User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) Cancel-Lock: sha1:UBvs4ne2u986X3rSQhNtRM1sWvY= Xref: csiph.com comp.programming:2335 BGB writes: > On 10/12/2012 3:30 PM, BartC wrote: >> And the real reason for 80 bits, is probably that the mantissa is >> exactly 64 >> bits; that makes it attractive for the same sorts of reasons that 64-bit >> processors are more popular than 52-bit ones. An 80-bit floating-point >> value can also represent a 64-bit integer exactly (signed *or* unsigned >> I believe). It's worth bothering with! > > but it is an inconvenient size in that it requires 80 bits to store, > which is not much more than 64 bits, but kills power-of-2 alignment, > whereas a 64-bit double is still aligned by a power-of-2. The 8087, that introduced this 80-bit format, was coupled with the 8086, which did not benefit from alignment beyond 16 bits. And the 8088 that the 8087 was perhaps more often coupled with did not benefit from alignment beyond 8-bit.