siblingPosition ranked a numbered node among its parent's matching children by
scanning the child list up to the node, counting matches. Run for every node of
a wide list, numbering was O(n^2): the default xsl:number over 8000 list items
took ~3.5s.
The count test is the same for every candidate of one xsl:number call, so cache
per parent and count pattern the one-based rank of each matching child, built
once. Each node's rank is then an O(1) lookup. The transformer holds the cache
across the whole transform; the count test itself is already O(1) through the
match cache, so building a parent's ranks is linear in its children. The numbers
are identical (a node's rank among matching siblings is 1 + the matching
siblings before it).
The 8000-item numbering drops ~3.5s to ~0.04s (~90x), quadratic to linear. The
full suite, the W3C XSLT and Apache Xalan corpora, and the WASM build stay
green; XSLTNumberSingleTests pins single, partial-match, and multiple-level.
Mihaela Mihaljevic
8f992a8897