Hi Ticker, attached patch implements also a table driven decoder for the adria topo map. The tree decoder and the table decode give the same values. I learned that I need this (hardcoded) array for Topo Adra int[] minCodes = {0,0,0,0,0,0,5,6,3,2,3,3,3,4,3,4,5,6,6,3,0}; I think these numbers are encoded in the struct bytes, but one has to shift the values. The shift amount is calculated by shift = maxDepth - depth. So, 06 00 00 | struct/mask for depth 19 ??? gives 6 >> (20-19) = 3 18 00 00 | struct/mask for depth 18 ??? gives 24 >> (20-18) = 4 ... 00 40 01 | struct/mask for depth 6 ??? gives 81920 >> (20 - 6) = 5 Found this last night, the patch doesn't implement this yet. I'll check your ideas about bytes 0..2. Those are the last which I don't understand. Gerd ________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap@jagit.co.uk> Gesendet: Dienstag, 28. Dezember 2021 01:18 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] [mkgmap-svn] Commit r572: MDR16 is some kind of codebook. Hi Gerd So, in the first byte of each prefix table entry, the bottom bit =1 means push 0-n bits back, =0 means need to get extra bits to decode. In both cases the value is >>1 and biased in a strange way. In most cases variable numbers of bits will be needed, but the minimum is known. Value of 0 means might need to get bits up to the max encoding length. Have you come up with a meaning for the second byte of the prefixes where it isn't a direct character. I see what you mean about byte 4. I don't follow what you mean about byte 6 and the length of the last block. Other static info that omight be encoded in bytes 0, 1 & 2 could be: 1/ version/subversion 2/ initial bits to read, giving size of prefix table (all 5 so far) 3/ includes refs to mdr29/30 &| 30/31. Which of your test maps have these sections? Ticker On Sun, 2021-12-26 at 19:39 +0000, Gerd Petermann wrote:
Hi Ticker,
a few more patterns: byte 4 seems to relate to the highest stat value in the rows with even stat values. I see e.g 0x0f and 0x1c or 0x0a and 0x1b. The formula: byte at 4 = highest /2 + 1
byte 6 (x) is related to the number of bytes (y) in the last block. (x = y * 2+ 1) I see e.g. 0x6b (107) and 53 bytes or 0x6d (109) with 54 bytes or 0x5d (93) and 46 bytes.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Gerd Petermann <gpetermann_muenchen@hotmail.com> Gesendet: Donnerstag, 23. Dezember 2021 20:53 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] [mkgmap-svn] Commit r572: MDR16 is some kind of codebook.
Hi Ticker,
reg. "stat": my rule is a bit different but the result is the same: for all odd values: depth = usedBits = stat >> 1;
val is the 2nd byte. for even stat values and rows where stat == val << 1 the decoder has to read exactly 1 more bit to decide which character was encoded. I've not yet understood how the stat or the val field can be used to find the correct entry in the byte array with the characters.
So, maybe the stat value should be shifted to the right to make some sense.
Gerd
________________________________________ Von: mkgmap-dev <mkgmap-dev-bounces@lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap@jagit.co.uk> Gesendet: Donnerstag, 23. Dezember 2021 15:56 An: Development list for mkgmap Betreff: Re: [mkgmap-dev] [mkgmap-svn] Commit r572: MDR16 is some kind of codebook.
Hi Gerd
Maybe the "is always 8" is the character width.
I think I understand parts of it.
Read 5 bits and look up, giving 2 bytes. if first 3/5/6/9/b the final char in the second byte and return (b- first)/2 to the bit stream. Otherwise the combination somehow indicate a minimum number of more bits to read and where to start searching. maybe the 'struct for level' 1 or 2 bytes is a bit flag of which levels to look in. I notice (in topo_fr) it is normally a single or adjacent bits except for 0xa, but there are no chars at level 19
prefix 0 doesn't quite follow the rules
Ticker
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