Method exact_asymmetric_distance

nodedb-codec/src/vector_quant/bbq.rs:293–303

Exact asymmetric L2 distance using the dequantized stored vector. The query is exact centered FP32 (`q.centered`). The stored vector is reconstructed from its sign bits and `residual_norm` via [`BbqCodec::dequantize`]: each dimension ≈ ±residual_norm / √dim. This is the high-fidelity asymmetric path invoked during rerank on the `oversample × top_k` candidates returned by the coarse Hamming pass.

(&self, q: &BbqQuery, v: &BbqQuantized)

    /// This is the high-fidelity asymmetric path invoked during rerank on the
    /// `oversample × top_k` candidates returned by the coarse Hamming pass.
    fn exact_asymmetric_distance(&self, q: &BbqQuery, v: &BbqQuantized) -> f32 {
        let header = v.0.header();
        let recon = Self::dequantize(v.0.packed_bits(), header.residual_norm, self.dim);
        // L2(q.centered, recon)
        q.centered
            .iter()
            .zip(recon.iter())
            .map(|(&a, &b)| (a - b) * (a - b))
            .sum::<f32>()
            .sqrt()
    }
}

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