abseil-inspired fast string hash: 1.87x at 50% load (up from 1.74x)#5
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joshuaisaact wants to merge 192 commits intomainfrom
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abseil-inspired fast string hash: 1.87x at 50% load (up from 1.74x)#5joshuaisaact wants to merge 192 commits intomainfrom
joshuaisaact wants to merge 192 commits intomainfrom
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…oad)" This reverts commit b725080.
…load)" This reverts commit 65aee5b.
This reverts commit 93a99b8.
This reverts commit e5abd48.
…lot)" This reverts commit 32dd07a.
- src/string_hybrid.zig: StringElasticHash with wyhash, same tiered architecture - src/autobench-strings.zig: Zig benchmark with 16-byte hex keys - bench-abseil-strings.cpp: abseil benchmark with string_view keys - bench-strings.sh: comparison runner - build.zig: added string test and benchmark steps
… access Shuffled hit lookup gaps at 1M (string_view keys, 16-byte hex): 10%: 1.97x 25%: 1.86x 50%: 1.74x 75%: 1.61x 90%: 1.50x 99%: 1.36x The advantage is LARGER than u64 keys because: - Fingerprint filtering saves expensive 16-byte memcmp comparisons - Both sides pay more for wyhash, but our table structure saves more per probe
…, sizes, despite slower hash
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Why
Our wyhash was 33% slower than abseil's hash for 16-byte strings. This PR ports abseil's fast path for 9-16 byte keys: two overlapping u64 reads + a single 128-bit multiply.
What
Replaced
Wyhash.hash(0, key)with a customfastStringHashinstring_hybrid.zigthat uses abseil's approach for 9-16 byte keys (the common case for our 16-byte hex keys). Falls back to wyhash for other lengths.Results (shuffled hit lookup, 1M, 16-byte string keys)
As predicted, the hash accounts for ~4-7% of the total advantage. The remaining 80-87% is structural (tiered metadata density).
References
/usr/include/absl/hash/internal/hash.hlines 960-1064