[mkgmap-dev] [mkgmap-svn] Commit r572: MDR16 is some kind of codebook.

Thu Dec 23 08:31:12 GMT 2021

Hi Gerd

I guessed that it was the \0 that cut the file off.

You mean something like answer 5 here:

https://stackoverflow.com/questions/759707/efficient-way-of-storing-huffman-tree

I looked at this earlier trying to work out if it was relevant but
didn't make it fit - I should have tried harder.

I still haven't spotted anything to determine the length of the 2 /3
byte in before and in the struct for {length}

Ticker

On Thu, 2021-12-23 at 01:17 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> sorry, just noticed that something went wrong with copy&paste because
> of the \0 character.
> Anyway, I think I understand the meaning of the part with the prefixes.
> I assume that Garmin reads the first 5 bits and uses this value as an
> index into a table
> which directly follows the first array. This 2nd table is a 32x2 lookup
> table, where the 2nd byte gives the value
> and the first byte some kind of status info which is used to position
> the bit reader.
> This would explain the repeating characters. Something like this:
> 
> --------- MDR 16 (decompression codebook Huffman tree) ----------------
> ---------
> 000002b6 | 000000 | 4a                      | ???