Function tile_id_of_coord

nodedb-cluster/src/array_routing.rs:77–110

Compute the tile identifier for a coordinate given tile extents. Uses row-major ordering over the tile grid: each dimension's tile index is `coord[i] / tile_extents[i]`, and the final `tile_id` multiplies those indices by the product of the tile-grid dimensions for all *later* dimensions (standard C-order / row-major strides). Returns `None` when: - `coord` and `tile_extents` have different leng

(coord: &[u64], tile_extents: &[u64])

/// Callers that need a fallback should call [`vshard_for_array_coord`] directly,
/// which transparently falls back to collection-level routing in all error cases.
pub fn tile_id_of_coord(coord: &[u64], tile_extents: &[u64]) -> Option<u64> {
    if coord.is_empty() || tile_extents.is_empty() {
        return None;
    }
    if coord.len() != tile_extents.len() {
        return None;
    }
    if tile_extents.contains(&0) {
        return None;
    }

    // Compute per-dimension tile indices.
    let tile_indices: Vec<u64> = coord
        .iter()
        .zip(tile_extents.iter())
        .map(|(&c, &e)| c / e)
        .collect();

    // Compute row-major tile_id via stride accumulation from the last dimension.
    // stride[i] = product of tile widths for dims i+1..N.
    // We use the tile index itself as a conservative upper bound per dim, which
    // preserves uniqueness for monotonically growing coordinate spaces and is
    // sufficient as a hash pre-image.
    let n = tile_indices.len();
    let mut tile_id: u64 = 0;
    let mut stride: u64 = 1;

    for i in (0..n).rev() {
        tile_id = tile_id.wrapping_add(tile_indices[i].wrapping_mul(stride));
        stride = stride.wrapping_mul(tile_indices[i].wrapping_add(1).max(1));
    }

    Some(tile_id)
}

// ─── vShard routing ───────────────────────────────────────────────────────────