The semantic pass kept four dense 768-float vectors resident per function
(ri/api/type/deco = 12.3 KB per func, ~9.4 GB transient on the linux kernel)
solely so candidate pairs could be cosine-scored after LSH. Replace the
resident floats with 4-bit quantized codes (~0.5 KB each, ~6x): new
src/semantic/rotsq.{h,c} — rotated scalar quantization from the RaBitQ
family of algorithms (Gao et al., SIGMOD 2024/2025), implemented from the
papers in plain C11 (no Eigen/library dependency): a deterministic
XXH3-seeded +-1 diagonal followed by a Fast Walsh-Hadamard rotation
(768 -> 1024 padded) spreads vector mass so per-vector scalar quantization
is near-optimal; the inner product is recovered from the codes with the
exact SQ expansion (one u8 integer dot + four multiplies) — a deterministic
pure function of the codes. Named rotsq, not rabitq: this is the family
core, not the papers' exact codebook construction.
Producers build each dense vector in a worker-local buffer, encode, and
discard; the int8 qvec export is unchanged. LSH signatures are computed
from DEQUANTIZED codes against hyperplanes in the rotated basis — random
hyperplanes are basis-agnostic, so no dense originals are retained and the
phase structure is untouched.
Estimator quality gated by sem_rotsq_ip_error_bounds (seeded vectors:
mean error < 1%, max < 4% of unit scale, ASan-green). Effect on output:
multi-threaded determinism preserved (xfs: two runs byte-identical);
SEMANTICALLY_RELATED edges shift once as scores move within ~1% of the
0.75 threshold (xfs: ~130 -> 203; sampled new pairs are high quality —
alloc/free, read-verify and collapse/insert families).
Suites: semantic 33 (incl. the new estimator gate), simhash 24,
pipeline 216 — zero failures.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
Martin Vogel