Module vector_quant 

Vector quantization codec family — binary, ternary, 4-bit scalar, residual, and unified layout types shared across HNSW hot-path, IVF-PQ, and BBQ.

Modules

bbq

BBQ — Better Binary Quantization (Elasticsearch 9.1, mid-2025).

codec

Dual-phase VectorCodec trait — the seam that makes future quantization algorithms drop-in additions rather than engine rewrites.

hamming

Shared SIMD Hamming-distance kernel with runtime CPU-feature dispatch.

layout

Unified Quantized Vector layout — the cache-aligned superset format that absorbs binary / ternary (BitNet 1.58) / 4-bit scalar / residual codecs without polymorphic indirection in the hot path.

opq

Optimized Product Quantization (OPQ) — Non-Para OPQ via iterative SVD-Procrustes rotation that minimizes PQ reconstruction error, yielding 10–20% recall improvement over vanilla PQ at equal memory.

opq_kmeans

Lloyd’s k-means for OPQ codebook training.

opq_rotation

Shared utilities for OPQ codebook training.

rabitq

RaBitQ — 1-bit quantization with O(1/√D) MSE error bound (SIGMOD 2024).

ternary

BitNet b1.58 ternary quantization codec.