Replaces the prior Robin-Hood open-addressing implementation with
Verstable (https://github.com/JacksonAllan/Verstable), a 2024 state-
of-the-art C hash table. The public API in foundation/hash_table.h
is UNCHANGED — CBMHashTable is now an opaque type and all 14
production callers (graph_buffer, registry, pipeline passes,
service_patterns, watcher, semantic, etc.) get the new impl
transparently. str_intern.c keeps its specialised (ptr+len) hash —
different semantics, not a clean swap target.
Why: per-sub-phase profiling pinpointed cbm_pipeline_lsp_target_node
and cbm_registry_resolve as the dominant resolve_calls cost. Both
ultimately hit cbm_ht_get; both run millions of times on a kubernetes
index. Verstable's key innovations target exactly this:
* 4-bit hash-fragment metadata in a uint16_t sidecar array lets
chain walks skip most key comparisons WITHOUT touching the
bucket payload (cache wins on hot lookups).
* Quadratic probing with per-bucket displacement chains (not linear
Robin-Hood psl).
* Tombstone-free deletion that moves at most one existing key.
Vendored at internal/cbm/vendored/verstable/verstable.h (2069 lines,
84KB, MIT). Wrapped as a const char* → void* template inside
hash_table.c. The header struct is opaque (forward declaration only);
audited the entire tree — no caller accesses internals or takes
sizeof(CBMHashTable), so opacity is safe.
Test refactor: test_hash_table.c had two impl-specific tests:
* ht_robin_hood_bounded_psl — Robin-Hood specific; removed.
ht_stress_10000 covers the functional equivalent.
* ht_power_of_two_capacity — renamed ht_create_small_capacity,
replaced struct probes with a functional insert+lookup check.
ht_create_capacity_zero/one similarly de-internalised.
Benchmark on kubernetes (12 workers, 20,650 files):
- parallel_resolve wall: 36,376 -> 27,217 ms (-25.2%)
- pipeline.done total: 61,485 -> 51,745 ms (-15.8%)
- registry_build: ~1,000 -> 779 ms (faster — registry uses
cbm_ht_set heavily during build)
- All 3,615 tests pass; hash_table suite 100% green
- ASan/UBSan/SEGV: none
- Peak RSS: ~6.83 GB
- Graph: nodes 297,082 -> 297,102 (+20, 0.007%), edges 1,155,444 ->
1,154,025 (-1,419, -0.12%) — within tolerance; minor delta likely
from hash-iteration-order differences affecting tie-breaks in
resolution. Sanity (zod/serilog): nodes exact, edges within 0.1%.
Cumulative trajectory from broken-state baseline ~35 min on K8s ->
51.7s wall = ~40x total speedup.
Enforce WarningsAsErrors: '*' with zero suppressions of entire check categories.
All non-FP warnings fixed at source; true false positives get per-instance NOLINT
with reasoning. Fixes include: braces around statements (1679), isolate declarations
(75), explicit casts for multilevel pointer conversions, missing includes, function
parameter documentation via NOLINT, and proper NOLINTBEGIN/NOLINTEND nesting.
Complete C implementation of the indexing pipeline (src/), parallel worker
pool, graph buffer with merge support, SQLite writer, and 1893-test suite.
Linter setup: zero warnings from clang-tidy (all checks enabled, no NOLINT
suppressions), cppcheck, and clang-format. All issues fixed at source —
proper headers for external linkage, GROW_ARRAY macro restructured to
eliminate type parameter, null-deref paths guarded, named intermediates
for suspicious-argument checks.
Martin Vogel