[mkgmap-dev] Polyline base optimisation

Thu Apr 8 16:34:53 BST 2021

Hi Gerd

I could have changed it to this, but it is looking for lowest val <= 0
and highest val >= 0 so 0 seemed the better choice.

The slight improvement is because it gives up after 2 tries that don't
show improvement, and before, for unsigned, one of these tries was
wasted.

Ticker

On Thu, 2021-04-08 at 15:11 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> Funny, I would have used Integer.MinValue for maxDx/maxDy to make it
> less confusing.
> Do you have an explanation for the change in size? My understanding
> is that your patch just skips a test which will never find a better
> encoding?
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> Gesendet: Donnerstag, 8. April 2021 13:58
> An: mkgmap development
> Betreff: [mkgmap-dev] Polyline base optimisation
> 
> Hi Gerd
> 
> If starting with unsigned deltas in polyline encoding, and attempting
> to reduce the length by testing reduced x/yBase values, there isn't
> any
> point in testing Base-1, as the normal number of bits will be the
> same
> (added sign bit) and there will be some overflows.
> 
> Patch attached to change this - it gives me a very slight reduction
> in
> RGN size and might give a performance improvement (I didn't detect
> any).
> 
> I've also fixed a couple of log. logic errors and changed minDx/y
> initial to 0, which is much less confusing because they are symmetric
> with maxDx/y which do use 0.
> 
> Ticker
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