nodedb_vector/distance/
mod.rs

1// SPDX-License-Identifier: Apache-2.0
2
3//! Distance metrics for vector similarity search.
4
5pub mod scalar;
6pub mod simd;
7
8pub use scalar::*;
9
10/// Compute distance between two vectors using the specified metric.
11///
12/// Dispatches to SIMD kernels (AVX-512, AVX2+FMA, NEON) where available;
13/// falls back to scalar implementations on other architectures.
14#[inline]
15pub fn distance(a: &[f32], b: &[f32], metric: DistanceMetric) -> f32 {
16    assert_eq!(
17        a.len(),
18        b.len(),
19        "distance: length mismatch (a.len()={}, b.len()={})",
20        a.len(),
21        b.len()
22    );
23    let rt = simd::runtime();
24    match metric {
25        DistanceMetric::L2 => (rt.l2_squared)(a, b),
26        DistanceMetric::Cosine => (rt.cosine_distance)(a, b),
27        DistanceMetric::InnerProduct => (rt.neg_inner_product)(a, b),
28        DistanceMetric::Manhattan => manhattan(a, b),
29        DistanceMetric::Chebyshev => chebyshev(a, b),
30        DistanceMetric::Hamming => hamming_f32(a, b),
31        DistanceMetric::Jaccard => jaccard(a, b),
32        DistanceMetric::Pearson => pearson(a, b),
33        // Unknown future metric — fall back to L2.
34        _ => (rt.l2_squared)(a, b),
35    }
36}
37
38/// Batch distance: compute distances from `query` to each candidate.
39///
40/// Returns `(index, distance)` pairs sorted ascending, truncated to `top_k`.
41pub fn batch_distances(
42    query: &[f32],
43    candidates: &[&[f32]],
44    metric: DistanceMetric,
45    top_k: usize,
46) -> Vec<(usize, f32)> {
47    let mut dists: Vec<(usize, f32)> = candidates
48        .iter()
49        .enumerate()
50        .map(|(i, c)| (i, distance(query, c, metric)))
51        .collect();
52
53    if top_k < dists.len() {
54        dists.select_nth_unstable_by(top_k, |a, b| {
55            a.1.partial_cmp(&b.1).unwrap_or(std::cmp::Ordering::Equal)
56        });
57        dists.truncate(top_k);
58    }
59    dists.sort_unstable_by(|a, b| a.1.partial_cmp(&b.1).unwrap_or(std::cmp::Ordering::Equal));
60    dists
61}
nodedb_vector/distance/mod.rs

nodedb_vector/distance/
mod.rs
