Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!lethe!yunexus!davecb
From: davecb@yunexus.YorkU.CA (David Collier-Brown)
Newsgroups: comp.arch
Subject: Re: 64 bits for times....
Message-ID: <14423@yunexus.YorkU.CA>
Date: 29 Aug 90 12:28:24 GMT
References: <11187@alice.UUCP> <3300165@m.cs.uiuc.edu> <2470@crdos1.crd.ge.COM>
Organization: York U. Computing Services
Lines: 42



>In article <3300165@m.cs.uiuc.edu> gillies@m.cs.uiuc.edu writes:

>  [ strong statement on stupidity of ns dating ]

>| Also, tell me when it will be possible to synchronize all the computer
>| clocks with a nano-second accuracy atomic clock.  How will such a
>| clock be reset later?

>  I guess the first question is when will there be a benefit from doing
>so? And how long will it stay in sync?
>| 
>| My conclusion:  ISO should specify a nanosecond relative timer, and a
>| much coaser absolute timer (like milliseconds).

davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes:
>  The timer should not be more accurate than the accuracy of the
>setting. Unless there's a good way to set such a timer within a ms
>*repeatably* then why worry about how accurately you can measure it? The
>relative timer is important, the absolute timer leads people to believe
>they have accuracy they don't.

  Er, this is a solved problem in software engineering... You have an
architecture-specific constant that tells you how may bits are significant
to the ``right'' of the decimal point ,and a function that returns only
those bits non-zero.
  The application can use a constant-size time variable, and discover
how much of it is significant when necessary.

  If I were writing this in an object-oriented language (:-)), I'd
define it thusly:
	declare clock_$absolute_machine_time entry() fixed decimal (72,36),
		clock_$accuracy entry() fixed binary (6);

--dave (pardon me if I got the PL/1 wrong, but I couldn't resist
	bring up the 1970s ``state of practice'' solution) c-b
-- 
David Collier-Brown,  | davecb@Nexus.YorkU.CA, ...!yunexus!davecb or
72 Abitibi Ave.,      | {toronto area...}lethe!dave 
Willowdale, Ontario,  | "And the next 8 man-months came up like
CANADA. 416-223-8968  |   thunder across the bay" --david kipling