good stuff

server-rs/src/parsing/h3.rs

@@ -1,4 +1,5 @@
 use axum::http::StatusCode;
+use rustc_hash::FxHashMap;
 use tracing::warn;
 
 use crate::consts::{H3_PRECOMPUTE_MAX, H3_REQUEST_MAX, H3_REQUEST_MIN};
@@ -45,6 +46,28 @@ pub fn cell_for_row(
     )
 }
 
+/// Like cell_for_row but caches parent lookups in the provided map.
+#[inline]
+pub fn cell_for_row_cached(
+    row: usize,
+    precomputed: &[u64],
+    h3_res: h3o::Resolution,
+    need_parent: bool,
+    cache: &mut FxHashMap<u64, u64>,
+) -> u64 {
+    let max_cell = precomputed[row];
+    if !need_parent || max_cell == 0 {
+        return max_cell;
+    }
+    *cache.entry(max_cell).or_insert_with(|| {
+        let cell = h3o::CellIndex::try_from(max_cell).expect("precomputed H3 cell must be valid");
+        u64::from(
+            cell.parent(h3_res)
+                .expect("parent resolution must be valid"),
+        )
+    })
+}
+
 /// Whether the given resolution requires computing a parent from precomputed cells.
 #[inline]
 pub fn needs_parent(resolution: u8) -> bool {