[mkgmap-dev] Please try and report results of Huffman compression

Sun Jan 16 12:37:21 GMT 2022

Hi Gerd

I'm just starting to look at this, but won't be able to do much today,
but some initial findings:

If just making gmapi from .img, unless --code-page is given it doesn't
do compression, however the Mdr generated with the expected charset.

MdrCheck and MdrDisplay, including string dump, look good

Ticker

On Sat, 2022-01-15 at 15:59 +0000, Gerd Petermann wrote:
> Hi all,
> 
> during the last weeks Ticker and I decoded Garmin's String compression
> of the global index for the PC (the *_mdr.img) .
> In the mdr2 branch I've coded support for that in mkgmap and I think
> its ready for a first beta test.
> 
> It works with codepages 1250 ..1258 or 65001. 
> I've no idea how the 2-byte pages work, but Garmin seems to support
> that, too. Maybe I'll work on this later.
> 
> The branch version produces around 200 lines of diagnostic output to
> show what happens when compression is enabled.
> This will be changed to debug level later.
> 
> The encoding is enabled by default, special option --x-no-mdr15-
> compression can be used to turn it off.
> 
> Note that the size of the *_mdr.img file will be smaller (which is esp.
> intersting for those who get close to the 2G limit)
> Note also that a zipped *_mdr.img can and will be larger since zip
> cannot remove as much redundancy. 
> Note also that this branch includes the changes from the faster-mp
> branch and introduces a few changes 
> which are relavant for --lower-case maps.
> 
> How to test?
> Install the map in MapSource and check if you see any unexpected
> characters in the result lists or maybe even crashes while searching.
> If so, please try the same input files with the --x-no-mdr15-
> compression to verify if this is caused by compression or maybe other
> changes.
> 
> Please don't yet publish the maps, but let me know if you see anything
> unexpected. Some changes reg. lower-case in this branch are still
> experimental.
> 
> The binary is here:
> https://www.mkgmap.org.uk/download/mkgmap-mdr2-r4865.zip
> 
> If you see errors which are caused by compression, please attach the
> diagnostic output.
> 
> @Ticker: Please review the source.
> 
> Gerd
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