EntityExpander.expand located the next '&', '<', and ';' with String.firstIndex
over graphemes, so every literal byte of a run was decoded into a grapheme just
to look for a one-byte marker. All three markers are ASCII, so a UTF-8 index is
a valid string index: scan over raw.utf8 instead, and the found index still
subscripts the string directly (the marker byte is never a continuation byte,
so its index lands on a scalar and grapheme boundary).
The decoded text is unchanged, including runs where the marker follows
multibyte UTF-8: a precomposed letter, a combining sequence, or an astral
character all leave the marker on a grapheme boundary.
Measured parse ~5.5% faster on the 20k-item generated corpus via a same-state
A/B (6.5x to ~6.1x slower than libxml2). Verified by EntityDecodeBulkTests
(extended with four multibyte-boundary cases), the W3C XML conformance corpora,
the Xalan XSLT gold-output corpus, the full suite, and the WASM build.
Mihaela Mihaljevic
6be96e51ce