dweiss commented on code in PR #14381:
URL: https://github.com/apache/lucene/pull/14381#discussion_r2006930601
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lucene/core/src/java/org/apache/lucene/util/automaton/RegExp.java:
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@@ -778,6 +786,53 @@ private int[] toCaseInsensitiveChar(int codepoint) {
}
}
+ /**
+ * Expands range to include case-insensitive matches.
+ *
+ * <p>This is expensive: case-insensitive range involves iterating over the
range space, adding
+ * alternatives. Jump on the grenade here, contain CPU and memory explosion
just to this method
+ * activated by optional flag.
+ */
+ private void expandCaseInsensitiveRange(
+ int start, int end, List<Integer> rangeStarts, List<Integer> rangeEnds) {
+ if (start > end)
+ throw new IllegalArgumentException(
+ "invalid range: from (" + start + ") cannot be > to (" + end + ")");
+
+ // contain the explosion of transitions by using a throwaway state
+ Automaton scratch = new Automaton();
+ int state = scratch.createState();
+
+ // iterate over range, adding codepoint and any alternatives as transitions
+ for (int i = start; i <= end; i++) {
+ scratch.addTransition(state, state, i);
+ int[] altCodePoints = CaseFolding.lookupAlternates(i);
+ if (altCodePoints != null) {
+ for (int alt : altCodePoints) {
+ scratch.addTransition(state, state, alt);
+ }
+ } else {
+ int altCase =
+ Character.isLowerCase(i) ? Character.toUpperCase(i) :
Character.toLowerCase(i);
+ if (altCase != i) {
+ scratch.addTransition(state, state, altCase);
+ }
+ }
+ }
Review Comment:
I think this pattern is used in more than one place. Maybe it'd be nicer to
make CaseFolding.forAllAlternatives(altCase -> scratch.addTransition(state,
state, altCase)) and have all that logic for checking for alternatives embedded
in CaseFolding?
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