From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,31d67020d4b04d5b X-Google-Attributes: gid103376,public From: dennison@telepath.com Subject: Re: Simple Real_Time.Time_Span question Date: 1998/10/15 Message-ID: <705g81$g9s$1@nnrp1.dejanews.com>#1/1 X-Deja-AN: 401418426 References: <6vvsgo$rvo$1@nnrp1.dejanews.com> <700usk$cht$1@nnrp1.dejanews.com> <702b25$30a$1@nnrp1.dejanews.com> X-Http-Proxy: 1.0 x7.dejanews.com:80 (Squid/1.1.22) for client 204.48.27.130 Organization: Deja News - The Leader in Internet Discussion X-Article-Creation-Date: Thu Oct 15 18:51:45 1998 GMT Newsgroups: comp.lang.ada X-Http-User-Agent: Mozilla/4.05 [en] (WinNT; I) Date: 1998-10-15T00:00:00+00:00 List-Id: In article , eachus@spectre.mitre.org (Robert I. Eachus) wrote: > In article <702b25$30a$1@nnrp1.dejanews.com> dennison@telepath.com writes: > > > that can represent both 86,400 and 0.000_000_001, my poor > > calculations tell me you'd need at least 47 bits. On a 32-bit > > processor that would be tricky. > > You use 64-bits, and when necessary, multiprecision arithmetic. > Remember that on many 32-bit processors, addition and subtraction of > 64-bit numbers is either supported directly in the instruction set, or > through instructions like add-with-carry. Hmmm. I guess there's a bit of a hole in my education where multiprecision integer arithmetic is concerned. I assume an add-with-carry instruction has some way of handling when *two* bits need to be carried (eg: the msbit of both previous operands was a 1, and there was a carry-in to that bit-position). Or perhaps you have to add one to the second word of the result if there was a carry and the msbit of the first word of the result is 0? Either way it sounds like simple arithmetic will be significantly slower for a Duration implemented in this way than one would typically expect of a predefined type. I can certianly see where compiler vendors for some real-time platforms might decide *not* to do that. So I don't think I can safely assume that a Time_Span of a few microseconds will translate well into Duration on any platform that this code may end up on (or even its current platform, 'till I find out for sure). -- T.E.D. -----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own