[mkgmap-dev] Possible optimization of StyledConverterFrom GerdP gpetermann_muenchen at hotmail.com on Thu Jan 5 05:41:25 GMT 2012
Steve, WanMil, the discussion about a prepro for styles inspired me to think about a compiler/optimizer for style rules. The point that I have in mind is this: Style files typically have many different rules starting with e.g. highway=* & ... The current iplementation in RuleSet.java and RuleIndex.java will first create a set of all rules that might match for the existing tags of a given element. Next, it processes each rule until the element is done. Let's assume an element that has tag "highway" and maybe 4 other tags If we have twenty rules with highway=* and none of them matches, we'll call getTag("highway") twenty times, always with the same result. Although getTag() is not very complex, it still means a lookup in a hash table. I see two possible optimizations here: 1) Combine rules that start with the same expression, e.g. highway=*, so that we don't evaluate tags again and again. In the past I used parser generator tools like lexx+yacc. I have the feeling that the rule interpretation is also something that could be done by a table driven parser. 2) A bit off-topic: Use a short instead of a String for the keys of Tags. I think even complex styles will not use more than a few hundred different tag keys. If all used tag keys are stored in an array, we can refer to the position in that array. Some weeks ago I coded that and it turned out to save some CPU cycles because Tags.keyPos() is simpler, but it also required changes in many sources and I found other patches providing more improvement with smaller changes. What do you think about this? Gerd P.S. A storm kept me awake all night long, so maybe I am writing nonsense :-O -- View this message in context: http://gis.638310.n2.nabble.com/Possible-optimization-of-StyledConverter-tp7153308p7153308.html Sent from the Mkgmap Development mailing list archive at Nabble.com.
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