Version mkgmap-r4185 was committed by gerd on Sun, 06 May 2018
tags5.patch: Improve the RuleIndex.
Attached patch reduces again the number of evaluated rules, but should still
evaluates all necessary rules.
The old index still returned too many rules. Let's look at the example that I
added as unit test. Set of rules:
0: a=* {set b=1}
1: b=1 {set c=1}
2: d=2 {set c=2}
3: c=* {set a=2}
4: c=1 {set d=2}
5: c=2 {set d=1}
6: d=1 [0x10401 resolution 24]
7: d=2 [0x10402 resolution 24]
Assume we have no index and an element with only one tag a=1. We check each
rule:
Rules 0 matches and sets b=1
Now 1 matches and sets c=1
Rule 2 doesn't match.
Rule 3 matches and sets a=2
Rule 4 matches and sets d=2
Rule 5 doesn't match.
Rule 6 doesn't match.
Rule 7 matches.
The index is used to reduce the number of evaluated rules. In the best case it
should return rules 0,1,3,4, and 7 for the given element.
But the current code returns all rules because it thinks that rule 4 can set
d=2 and therefore rule 2 might be triggered (which is wrong).
The patch changes the index to recognizes the order of the rules which change
tags and therefore returns only the needed rules.
http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=4185
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