locate compared quote against every boundary with starts_with before
checking anything cheap, and allocated a fresh HashSet copy of the boundary
list on every call. Now compares the first byte before starts_with, and
binary-searches the already-sorted boundaries Vec for the end offset instead
of a second HashSet. The doc comment's stale "repeated-find shape below this
comment" line (referring to code this file no longer has) is replaced with
the real bound and a pointer to the new regression guard.
The existing guard (locate_completes_over_a_long_source) used a 64k-char
single-word source with only two boundaries, so it never exercised the
O(boundaries) shape the bound is about. locate_is_fast_over_many_boundaries_
and_a_long_quote adds a 528,000-char many-boundary source against a
264,000-char non-matching quote. Measured on this workstation (this test
alone, cargo test's own reported time): pre-fix ~0.31s, post-fix ~0.13s —
real, but well short of the 1.73s figure this task's own brief quoted for a
"528k against a 264k quote"; that number was not reproduced with this exact
input shape and is not claimed here.
Two rules had no test: locate_returns_the_leftmost_boundary_valid_candidate
(reversing the boundary walk returns the last candidate instead of the
first) and locate_refuses_an_empty_quote (removing the empty-quote guard
locates it as the vacuous span 0..0). Verified live: reversing the walk
returned start_byte 8 instead of 0; dropping the guard located "" as
Some(0..0); both reverted before commit.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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