Lwan’s web server replaces its kmod-derived hash table with a SwissTable-inspired design using memchr() for portable SIMD-like probing.
Key Takeaways
New design splits the hash into tophash (low 8 bits, used with memchr()) and startpos (next bits, power-of-two masked) for two-phase probing.
Uses a single flat group instead of SwissTable’s multi-group layout, trading some theoretical worst-case for simplicity and portability.
Deletion tombstones with \0 and triggers a full hash_resize() when load drops below 50%; in-place or lazy rehash is future work.
Hash function is FNV-1a or Intel CRC32 (hardware-dependent); author reports key equality succeeds on first probe in practice.
SELF_TEST() macros run on every debug boot, catching regressions during experimentation without a separate test harness.
Hacker News Comment Review
No substantive HN discussion yet; the one comment reflects on hash tables as a conceptual milestone in CS education rather than on the implementation itself.
