following(of:) and preceding(of:) rebuilt the entire document node list and ran
a linear firstIndex search for the context node on every call. Evaluated over
many context nodes (//x/following::y), that rebuild-and-search was quadratic: a
200-context following:: query over a 20k-element document took ~16s.
Share a per-evaluation DocumentNavigationCache: each document's ordered node
list and a node-to-index map are built once (the document is immutable during
evaluation) and reused, so the position lookup is O(1). following:: also skips
the context's contiguous subtree by index arithmetic (start = index + 1 +
descendant count) instead of scanning the tail and filtering every descendant
out. The selected nodes and their document order are unchanged.
The 200-context query drops ~16s to ~9s; the residual is the produced
node-set's own size (materialization), which is inherent to the axis. The full
suite, the W3C XPath/XSLT and Apache Xalan corpora, and the WASM build stay
green; FollowingPrecedingAxisTests pins the subtree skip, ancestor exclusion,
and the shared-cache multi-context path.
Mihaela Mihaljevic
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