Pivoting (or rather missing pivot)

Gary E. Miller gem at rellim.com
Thu Apr 27 15:17:06 UTC 2017

Yo Hal!

On Thu, 27 Apr 2017 02:53:37 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> >> Where does it do a pivot on the way to step_systime?  
> Gary said:
> > Stuck in a time warp again.  Not relevant to the bad reversion.
> > I'm not gonna go down that rabbit hole until we get this very
> > narrow problem dealt with.  
> Which problem do you think we are discussing?

The bad reversion is what I am discussing.

> > We have a well bounded problem with 2 inputs and 1 output.  No need
> > for external info to know if this function does what it is supposed
> > to do: step the clock by double.   
> step_system works as you describe it.  The problem is that it is
> being fed bad data.

Really?  Can you detail your assertion?

> The code Eric reverted does a pivot.  Right?

No.  It thinks it does a pivot, but you never pivot an offset, only
a timestaamp.  When you subtract one timestamp (with the implicit
term NTP_EPOCH) from another timestamp (with th eimplicit NTP_EPOCH)
then you have removed the term NTP_EPOCH.

No need to deal with it downstream any more.

>  We agree that the code
> is ugly. You claim it is not necessary.

And have shown my math to shot that.  Can you show any math to
prove me wrong?

>  All you have to do to get me
> to tell Eric it is not needed is show me where the pivot does take
> place.

See above.  No pivot needed.  Subtracting one timestamp from another
removes any constant that is in both terms.

> All the pivots are based on BUILD_EPOCH.  Right?  It's only used by 
> ntpcal_get_build_date()

No.  As you just said.  And out of scopy for this one discussion
that keeps going in circles.

> So unless I'm missing amd/or missed something, there is no pivot that
> covers l_fp data from NTP packets other than the one in step_systime()

Nor is there any need for one, in step_systime().  The 2s complement
subtraction works fine around the rollover.  I have posted here
arithetic samples that show that.

Please get a piece of apaer and just calculate several specific math
examples, as I have already posted on this discussion.  The number
do not lie.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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