meilisearch/milli/src/proximity.rs

use std::cmp;
use crate::{Attribute, Position};

const ONE_ATTRIBUTE: u32 = 1000;
const MAX_DISTANCE: u32 = 8;

pub fn index_proximity(lhs: u32, rhs: u32) -> u32 {
    if lhs <= rhs {
        cmp::min(rhs - lhs, MAX_DISTANCE)
    } else {
        cmp::min((lhs - rhs) + 1, MAX_DISTANCE)
    }
}

pub fn positions_proximity(lhs: Position, rhs: Position) -> u32 {
    let (lhs_attr, lhs_index) = extract_position(lhs);
    let (rhs_attr, rhs_index) = extract_position(rhs);
    if lhs_attr != rhs_attr { MAX_DISTANCE }
    else { index_proximity(lhs_index, rhs_index) }
}

pub fn extract_position(position: Position) -> (Attribute, Position) {
    (position / ONE_ATTRIBUTE, position % ONE_ATTRIBUTE)
}

pub fn path_proximity(path: &[Position]) -> u32 {
    path.windows(2).map(|w| positions_proximity(w[0], w[1])).sum::<u32>()
}