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Re: most portable way to compare file times

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BruceMcF wrote:

> On Nov 24, 2:58 pm, Alex McDonald <b...@rivadpm.com> wrote:
>> Which is why I suggested a string up-thread; cell size doesn't
>> matter, and resolution can be whatever you wish.
> 
> Its my preferred option, as I think of time stamping and timers as two
> different things, but if they're chasing up a ticks-since-epoch style
> semantic for porting among POSIX systems, I'd be happy if it was not
> unnecessarily impossible to implement by smaller systems.

I'm ok with the double ticks + single resolution (in ticks/s) solution.  
That one is dead easy to implement on a small system (you usually have 
some timer running where you can derive that value), and it is easy to 
process.  Note that on a small system, the "epoch" starts when you 
booted the device, since you often don't have a real time clock.

What I want to have:

* I don't want to impose the presence of a RTC, since it is not always 
possible
* I don't want to deal with strings, since this means some sort of 
primitive memory management (the make example will read the time stamps 
of a number of files, and then determine what to do, so a simple "is 
valid until the next call of this word" is not acceptable), and, on a 
small system, is a costly operator
* I want it be a primitive data type, so that you can use readily 
available operators
* I don't want to arbitrary limit the precision

So on a 64 bit system, femtoseconds since big bang is possible, on a 32 
bit system, microseconds since 1970.1.1T0:0:0Z won't wrap around soon, 
and on a 16 bit system, you might have 10 millisecond ticks since the 
last boot, which wraps around after one and a half year.  This is not 
the format you want your medical records in, but you won't create those 
on such a small system.

Networked systems always should synchronize their clocks with each other 
or with a common, high-quality clock source.  A network stack with time 
stamps can drop packets with "impossible" time stamps (an acknowledge 
for a packet timed before the package was sent, or after the acknowledge 
was received is impossible).

If the system has a real time clock and/or is synchronized to a global 
clock, then it should provide the information when the epoch started.  
Also, the ticks themselves should never go back.  I.e. if your clock 
needs to be synchronized by -1.2 seconds after boot, you correct the 
epoch starting point, not the actual tick counter.  If you figure out 
durning synchronization, that your so-called "nanoseconds" really are 
1002039185 ticks per second, just report that, and adjust the start of 
the epoch accordingly.  I'd propose the nominal clock starting point to 
be 1970.1.1T0:0:0Z.

This would be three words for the timing:

ticks ( -- d ) ticks since the epoch, monotonuous function, serializes 
the instruction stream, i.e. for any ticks ... ticks -, this is 
guaranteed to be <=0.
ticks/s ( -- u ) ticks per second
epoch ( -- d )  epoch started d ticks after 1970.1.1T00:00:00Z (negative 
means "before"), this is an optional word.

And for files, you have

file-ticks ( -- dc dw da ).

A standard program should assume that the timer may roll over.  How do 
we deal with small systems that have an RTC, but don't have enough bits 
to represent the epoch return value? 

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://bernd-paysan.de/

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most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-18 00:43 -0800
  Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-18 02:33 -0800
    Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-18 05:26 -0800
      Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-18 09:14 -0800
        Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-18 20:10 +0100
          Re: most portable way to compare file times Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-11-18 15:10 -0600
            Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-18 13:32 -0800
              Re: most portable way to compare file times anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-21 10:22 +0000
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-21 08:51 -0800
            Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-19 00:57 +0100
        Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-18 14:45 -0800
  Re: most portable way to compare file times "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-11-18 05:44 -0500
    Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-18 05:31 -0800
      Re: most portable way to compare file times anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-18 16:22 +0000
        Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-19 13:59 -0800
          Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-20 02:06 -0800
            Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-20 02:44 -0800
              Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-20 14:58 +0100
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-20 06:48 -0800
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-20 08:05 -0800
                Re: most portable way to compare file times Coos Haak <chforth@hccnet.nl> - 2011-11-20 20:53 +0100
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-20 12:21 -0800
                Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-21 21:03 +0100
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-21 17:32 -0800
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-21 17:45 -0800
                Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-24 15:48 +0100
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-24 09:34 -0800
                Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-24 11:58 -0800
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-24 17:25 -0800
                Re: most portable way to compare file times "Elizabeth D. Rather" <erather@forth.com> - 2011-11-24 20:56 -1000
                Re: most portable way to compare file times Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-11-25 04:15 -0600
                Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-25 04:17 -0800
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-25 05:47 -0800
                Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-25 08:58 -0800
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-25 11:43 -0800
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-25 11:12 -0800
                Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-25 05:39 -0800
                Re: most portable way to compare file times anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-27 14:34 +0000
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-27 08:46 -0800
                Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-25 04:32 -0800
                Re: most portable way to compare file times Alex McDonald <blog@rivadpm.com> - 2011-11-25 04:51 -0800
                Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-25 16:46 +0100
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-25 08:33 -0800
                Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-26 01:11 +0100
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-26 12:18 -0800
                Re: most portable way to compare file times Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-26 21:44 +0100
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-26 13:18 -0800
                Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-20 12:45 -0800
            Re: most portable way to compare file times Krishna Myneni <krishna.myneni@ccreweb.org> - 2011-11-20 07:49 -0800
        Re: most portable way to compare file times mhx@iae.nl (Marcel Hendrix) - 2011-11-20 09:45 +0200
      Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-18 10:42 -0800
  Re: most portable way to compare file times BruceMcF <agila61@netscape.net> - 2011-11-20 13:05 -0800

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