Method build_distance_table

nodedb-vector/src/quantize/pq.rs:158–174

Build an asymmetric distance table for a query vector. Returns `table[sub][centroid]` = distance from query's sub-vector to each centroid. Pre-computing this table makes distance evaluation O(M) per candidate instead of O(D). Charges `m * k * size_of:: ()` bytes to the governor (if set) before allocating the table.

(&self, query: &[f32])

    /// Charges `m * k * size_of::<f32>()` bytes to the governor (if set)
    /// before allocating the table.
    pub fn build_distance_table(&self, query: &[f32]) -> Result<Vec<Vec<f32>>, VectorError> {
        debug_assert_eq!(query.len(), self.dim);
        let total_bytes = self.m * self.k * size_of::<f32>();
        let _g = try_reserve_or_skip(&self.governor, total_bytes)?;
        let mut table = Vec::with_capacity(self.m);
        for sub in 0..self.m {
            let offset = sub * self.sub_dim;
            let sub_query = &query[offset..offset + self.sub_dim];
            let mut dists = Vec::with_capacity(self.k);
            for centroid in &self.codebooks[sub] {
                let d = l2_sub(sub_query, centroid);
                dists.push(d);
            }
            table.push(dists);
        }
        Ok(table)
    }

    /// Compute asymmetric distance using a precomputed distance table.
    ///