geopackage 0.6.0

//! Direct construction of SQLite RTree shadow-table contents.
//!
//! SQLite's RTree module has no bulk-load entry point, so the bulk build used to
//! insert every entry into a scratch RTree one row at a time and copy the
//! result. That insertion, not the surrounding work, dominated the build (3.03 s
//! of 4.87 s for 1M points), because each insert descends the tree and may split
//! nodes. This module skips the module entirely and writes the node blobs
//! itself, bottom-up, from a spatially sorted entry set.
//!
//! # Node format
//!
//! Taken from the RTree module's own documentation and its `rtreecheck`
//! implementation (SQLite 3.51.3, `sqlite3.c`). Every node blob is exactly
//! `node_size` bytes:
//!
//! ```text
//! bytes 0..2    big-endian u16: tree depth, root node only (0 = root is a leaf);
//!               unused on other nodes
//! bytes 2..4    big-endian u16: number of cells in this node
//! bytes 4..     cells, each 8 + 2*2*4 = 24 bytes for a 2-D index:
//!                 big-endian i64  rowid (leaf) or child node number (internal)
//!                 big-endian f32  min_x, max_x, min_y, max_y
//! remainder     zero padding
//! ```
//!
//! The root is always node 1. `%_rowid` maps each leaf entry's rowid to the node
//! holding it, and `%_parent` maps each non-root node to its parent.
//!
//! # What `rtreecheck` requires
//!
//! The gate runs `rtreecheck()` over the result, so the output must satisfy
//! exactly what it verifies: `4 + ncell * 24 <= node_size`; `min <= max` on
//! every dimension of every cell; every cell's bounds contained in its parent
//! cell's bounds; a `%_rowid` row per leaf cell and a `%_parent` row per
//! internal cell; and the counts of those two tables equal to the number of leaf
//! and internal cells respectively. It does **not** require any minimum node
//! fill, so nodes are packed full.

use crate::Result;
use crate::bulk::DEFAULT_FILL_FACTOR;

/// Bytes per cell in a 2-D RTree: an 8-byte id plus four 4-byte coordinates.
const BYTES_PER_CELL: usize = 24;
/// Bytes of node header: the depth/unused field and the cell count.
const NODE_HEADER: usize = 4;

/// Rounding constants from the RTree module, used to force a `f64` to a `f32`
/// that is no larger (`DOWN`) or no smaller (`UP`) than the original.
const RND_TOWARDS: f64 = 1.0 - 1.0 / 8_388_608.0;
const RND_AWAY: f64 = 1.0 + 1.0 / 8_388_608.0;

/// The largest `f32` that is `<= d`, matching the RTree module's
/// `rtreeValueDown`. Minimum bounds are rounded this way so the stored box never
/// excludes a value it should contain.
fn coord_down(d: f64) -> f32 {
    let f = d as f32;
    if f64::from(f) > d {
        (d * if d < 0.0 { RND_AWAY } else { RND_TOWARDS }) as f32
    } else {
        f
    }
}

/// The smallest `f32` that is `>= d`, matching the RTree module's
/// `rtreeValueUp`.
fn coord_up(d: f64) -> f32 {
    let f = d as f32;
    if f64::from(f) < d {
        (d * if d < 0.0 { RND_TOWARDS } else { RND_AWAY }) as f32
    } else {
        f
    }
}

/// One cell: an id (rowid for a leaf, child node number for an internal node)
/// and its `f32` bounds in the node-blob's coordinate order.
#[derive(Debug, Clone, Copy)]
struct Cell {
    id: i64,
    /// `[min_x, max_x, min_y, max_y]`, the order the RTree stores them in.
    bounds: [f32; 4],
}

impl Cell {
    /// The union of two cells' bounds. Both inputs are already `f32`, so the
    /// union is exact and needs no further rounding.
    fn union(bounds: &[f32; 4], other: &[f32; 4]) -> [f32; 4] {
        [
            bounds[0].min(other[0]),
            bounds[1].max(other[1]),
            bounds[2].min(other[2]),
            bounds[3].max(other[3]),
        ]
    }

    /// The centre of this cell, used for the spatial sort.
    fn centre(&self) -> (f64, f64) {
        (
            (f64::from(self.bounds[0]) + f64::from(self.bounds[1])) / 2.0,
            (f64::from(self.bounds[2]) + f64::from(self.bounds[3])) / 2.0,
        )
    }
}

/// Where a packed tree's rows are sent as it is built.
///
/// The tree is streamed rather than returned, so peak memory does not carry a
/// copy of every node blob and every rowid mapping on top of the entry set. At
/// 10M rows those two together are several hundred megabytes.
pub(crate) trait NodeSink {
    /// One `%_node` row: the node number and its blob.
    fn node(&mut self, nodeno: i64, blob: &[u8]) -> Result<()>;
    /// One `%_rowid` row: an indexed row's id and the leaf holding it.
    fn rowid(&mut self, rowid: i64, nodeno: i64) -> Result<()>;
    /// One `%_parent` row: a non-root node and its parent.
    fn parent(&mut self, nodeno: i64, parentnode: i64) -> Result<()>;
}

/// Hilbert index of a point on a 16-bit-per-axis grid over `extent`, used to
/// order entries so that nodes packed from consecutive entries are spatially
/// compact.
///
/// `extent` is the bounding box of the whole entry set rather than a fixed
/// domain, so this works for projected coordinate systems as well as degrees.
fn hilbert(x: f64, y: f64, extent: &[f64; 4]) -> u32 {
    const SIDE: u32 = 1 << 16;
    let norm = |v: f64, lo: f64, hi: f64| -> u32 {
        // A degenerate extent (all centres equal on this axis) or a non-finite
        // coordinate collapses to 0: order is then arbitrary but consistent.
        if !v.is_finite() || hi <= lo {
            return 0;
        }
        // `t` is clamped into [0, 1], so the scaled value is non-negative and
        // at most SIDE - 1.
        let t = ((v - lo) / (hi - lo)).clamp(0.0, 1.0);
        let scaled = t * f64::from(SIDE - 1);
        #[expect(
            clippy::cast_sign_loss,
            reason = "t is clamped to [0, 1], so scaled lies in [0, SIDE - 1] and is never negative"
        )]
        let index = scaled as u32;
        index.min(SIDE - 1)
    };
    let mut hx = norm(x, extent[0], extent[1]);
    let mut hy = norm(y, extent[2], extent[3]);

    let mut d: u32 = 0;
    let mut s: u32 = SIDE / 2;
    while s > 0 {
        let rx = u32::from((hx & s) > 0);
        let ry = u32::from((hy & s) > 0);
        d = d.wrapping_add(s.wrapping_mul(s).wrapping_mul((3 * rx) ^ ry));
        // Rotate the quadrant so the curve stays continuous.
        if ry == 0 {
            if rx == 1 {
                hx = s.wrapping_sub(1).wrapping_sub(hx);
                hy = s.wrapping_sub(1).wrapping_sub(hy);
            }
            std::mem::swap(&mut hx, &mut hy);
        }
        s /= 2;
    }
    d
}

/// Serialise one node into `blob`: the header followed by its cells,
/// zero-padded to `node_size`.
///
/// Writes into a caller-owned buffer so a build streams through one allocation
/// rather than one per node. The buffer is cleared on entry, so any previous
/// node's bytes are discarded.
fn encode_node_into(blob: &mut Vec<u8>, depth: u16, cells: &[Cell], node_size: usize) {
    blob.clear();
    blob.reserve(node_size);
    blob.extend_from_slice(&depth.to_be_bytes());
    // The cell count fits u16: callers cap cells at (node_size - 4) / 24.
    let count = u16::try_from(cells.len()).unwrap_or(u16::MAX);
    blob.extend_from_slice(&count.to_be_bytes());
    for cell in cells {
        blob.extend_from_slice(&cell.id.to_be_bytes());
        for coord in &cell.bounds {
            blob.extend_from_slice(&coord.to_be_bytes());
        }
    }
    blob.resize(node_size, 0);
}

/// The number of nodes at each level, leaves first, for `entries` entries at
/// `per_node` entries per node.
///
/// The last entry is always 1: the root. Returned so node numbers can be
/// assigned before anything is built, which is what lets the tree stream out
/// instead of being assembled in memory and renumbered at the end.
///
/// `per_node` is forced to at least 2. A fanout of 1 never reduces the level
/// size (`n.div_ceil(1) == n`), so the loop below would not terminate and would
/// grow `levels` until the process ran out of memory.
fn level_sizes(entries: usize, per_node: usize) -> Vec<usize> {
    let fanout = per_node.max(2);
    let mut levels = Vec::new();
    let mut count = entries.div_ceil(fanout).max(1);
    levels.push(count);
    while count > 1 {
        count = count.div_ceil(fanout);
        levels.push(count);
    }
    levels
}

/// Build an RTree over `entries` (`(rowid, [min_x, max_x, min_y, max_y])` in
/// `f64`) and stream it into `sink`.
///
/// `node_size` is the byte length the RTree module expects every node blob to
/// have; read it from the freshly created index rather than re-deriving it, so
/// the two cannot disagree.
///
/// `fill_factor` is the fraction of each node's capacity to use, in `(0, 1]`.
/// Packing full gives the smallest tree and the best queries, but leaves no room
/// for later inserts, which then split immediately. Lower it when the index will
/// be appended to after the bulk load.
///
/// An empty entry set still produces the root node, which the RTree module
/// requires to exist: a leaf at depth 0 with no cells.
pub(crate) fn pack_into<S: NodeSink>(
    entries: &[(i64, [f64; 4])],
    node_size: usize,
    fill_factor: f64,
    sink: &mut S,
) -> Result<()> {
    let capacity = node_size.saturating_sub(NODE_HEADER) / BYTES_PER_CELL;
    debug_assert!(capacity > 0, "node size {node_size} holds no cells");
    // Entries per node: the requested fraction of capacity, but never more than
    // the format allows and never fewer than 2.
    //
    // The lower bound is load-bearing, not defensive tidying. With a fanout of 1
    // each level above the leaves is the same size as the one below it, so the
    // tree has no top and [`level_sizes`] cannot terminate. A fill factor of 0,
    // a negative one, or NaN all reduce to 1 here without it: `NAN.clamp(..)` is
    // NaN, `NAN.round()` is NaN, and `NAN.max(1.0)` is 1.0.
    let per_node = {
        let requested = if fill_factor.is_nan() {
            DEFAULT_FILL_FACTOR
        } else {
            fill_factor.clamp(f64::MIN_POSITIVE, 1.0)
        };
        let scaled = (capacity as f64) * requested;
        #[expect(
            clippy::cast_sign_loss,
            reason = "`requested` is positive and at most 1, so `scaled` lies in [0, capacity] and rounds to a non-negative value"
        )]
        let rounded = scaled.round() as usize;
        rounded.clamp(2.min(capacity), capacity.max(1))
    };

    let mut blob = Vec::with_capacity(node_size);

    if entries.is_empty() {
        encode_node_into(&mut blob, 0, &[], node_size);
        return sink.node(1, &blob);
    }

    // Round each envelope outward to f32, exactly as the RTree module would, so
    // a stored box never excludes a geometry it must contain.
    //
    // The cells go straight into the keyed vector that will be sorted, with the
    // extent accumulated in the same pass and the Hilbert keys filled in after.
    // Building a separate cell vector first and draining it into this one costs
    // a second allocation the size of the whole entry set.
    let mut keyed: Vec<(u32, Cell)> = Vec::with_capacity(entries.len());
    let mut extent = [
        f64::INFINITY,
        f64::NEG_INFINITY,
        f64::INFINITY,
        f64::NEG_INFINITY,
    ];
    for &(id, [min_x, max_x, min_y, max_y]) in entries {
        let cell = Cell {
            id,
            bounds: [
                coord_down(min_x),
                coord_up(max_x),
                coord_down(min_y),
                coord_up(max_y),
            ],
        };
        let (cx, cy) = cell.centre();
        extent = [
            extent[0].min(cx),
            extent[1].max(cx),
            extent[2].min(cy),
            extent[3].max(cy),
        ];
        keyed.push((0, cell));
    }

    // Group the entries into leaf-sized, spatially compact sets by sorting on
    // the Hilbert index of each centre. Lee and Lee's OMT partitioning was
    // measured against this and is not better here: on uniformly spread data it
    // builds ~15% slower (it sorts at every level rather than once) with
    // slightly worse queries, and on clustered data the two are within noise.
    for (key, cell) in &mut keyed {
        let (cx, cy) = cell.centre();
        *key = hilbert(cx, cy, &extent);
    }
    keyed.sort_unstable_by_key(|(key, _)| *key);

    // Node numbers are fixed before anything is written. The root must be node
    // 1; everything else is numbered from 2 upward, leaves first, then each
    // level above. Knowing them up front is what allows streaming: a node can
    // be written as soon as it is built, because its parent's number is already
    // known.
    let levels = level_sizes(keyed.len(), per_node);
    let depth = u16::try_from(levels.len().saturating_sub(1)).unwrap_or(u16::MAX);
    // First node number used by each level.
    let mut level_base = Vec::with_capacity(levels.len());
    let mut next = 2_i64;
    for (index, count) in levels.iter().enumerate() {
        if index + 1 == levels.len() {
            // The top level is the single root node.
            level_base.push(1_i64);
        } else {
            level_base.push(next);
            next += i64::try_from(*count).unwrap_or(i64::MAX);
        }
    }

    // Level 0: the leaves, from the sorted entries.
    let base = level_base.first().copied().unwrap_or(1);
    let mut level: Vec<Cell> = Vec::with_capacity(levels.first().copied().unwrap_or(1));
    // Reused across leaves: `encode_node_into` wants the cells without their
    // sort keys, and one node's worth is at most `per_node` of them.
    let mut cells: Vec<Cell> = Vec::with_capacity(per_node);
    for (index, chunk) in keyed.chunks(per_node).enumerate() {
        let nodeno = base + i64::try_from(index).unwrap_or(0);
        cells.clear();
        cells.extend(chunk.iter().map(|(_, cell)| *cell));
        let mut bounds = cells.first().map_or([0.0; 4], |first| first.bounds);
        for cell in &cells {
            bounds = Cell::union(&bounds, &cell.bounds);
            sink.rowid(cell.id, nodeno)?;
        }
        encode_node_into(&mut blob, depth, &cells, node_size);
        sink.node(nodeno, &blob)?;
        level.push(Cell { id: nodeno, bounds });
    }

    // Internal levels, bottom-up. Each node's cells point at the level below,
    // whose numbers are already assigned, so `%_parent` can be written here.
    for height in 1..levels.len() {
        let base = level_base.get(height).copied().unwrap_or(1);
        let mut parents: Vec<Cell> = Vec::with_capacity(levels.get(height).copied().unwrap_or(1));
        for (index, chunk) in level.chunks(per_node).enumerate() {
            let nodeno = base + i64::try_from(index).unwrap_or(0);
            let mut bounds = chunk.first().map_or([0.0; 4], |first| first.bounds);
            for cell in chunk {
                bounds = Cell::union(&bounds, &cell.bounds);
                sink.parent(cell.id, nodeno)?;
            }
            let node_depth = u16::try_from(height).unwrap_or(0);
            encode_node_into(&mut blob, node_depth, chunk, node_size);
            sink.node(nodeno, &blob)?;
            parents.push(Cell { id: nodeno, bounds });
        }
        level = parents;
    }

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    /// A [`NodeSink`] that keeps everything, so tests can inspect the tree the
    /// streaming build would otherwise have written straight to SQLite.
    #[derive(Default)]
    struct Collected {
        nodes: Vec<(i64, Vec<u8>)>,
        rowid_map: Vec<(i64, i64)>,
        parent_map: Vec<(i64, i64)>,
    }

    impl NodeSink for Collected {
        fn node(&mut self, nodeno: i64, blob: &[u8]) -> Result<()> {
            self.nodes.push((nodeno, blob.to_vec()));
            Ok(())
        }
        fn rowid(&mut self, rowid: i64, nodeno: i64) -> Result<()> {
            self.rowid_map.push((rowid, nodeno));
            Ok(())
        }
        fn parent(&mut self, nodeno: i64, parentnode: i64) -> Result<()> {
            self.parent_map.push((nodeno, parentnode));
            Ok(())
        }
    }

    /// Pack into a [`Collected`] at full fill, the shape the tests assert on.
    fn pack(entries: &[(i64, [f64; 4])], node_size: usize) -> Result<Collected> {
        let mut collected = Collected::default();
        pack_into(entries, node_size, 1.0, &mut collected)?;
        Ok(collected)
    }

    /// Read the cells back out of an encoded node.
    fn decode_cells(blob: &[u8]) -> Vec<Cell> {
        let count = blob
            .get(2..4)
            .and_then(|b| <[u8; 2]>::try_from(b).ok())
            .map_or(0, |b| usize::from(u16::from_be_bytes(b)));
        let mut cells = Vec::with_capacity(count);
        for i in 0..count {
            let start = NODE_HEADER + i * BYTES_PER_CELL;
            let Some(raw) = blob.get(start..start + BYTES_PER_CELL) else {
                break;
            };
            let id = <[u8; 8]>::try_from(raw.get(0..8).unwrap_or_default())
                .map(i64::from_be_bytes)
                .unwrap_or_default();
            let mut bounds = [0.0f32; 4];
            for (n, slot) in bounds.iter_mut().enumerate() {
                let at = 8 + n * 4;
                *slot = <[u8; 4]>::try_from(raw.get(at..at + 4).unwrap_or_default())
                    .map(f32::from_be_bytes)
                    .unwrap_or_default();
            }
            cells.push(Cell { id, bounds });
        }
        cells
    }

    /// Every node blob is exactly `node_size` bytes, which the RTree module
    /// requires: it derives the node size from the root's length and rejects
    /// any node that differs.
    #[test]
    fn all_nodes_have_the_declared_size() {
        let entries: Vec<(i64, [f64; 4])> = (0..5000)
            .map(|i| {
                let f = f64::from(i);
                (i64::from(i), [f, f + 1.0, -f, -f + 1.0])
            })
            .collect();
        let packed = pack(&entries, 1228).unwrap();
        assert!(packed.nodes.len() > 1, "expected a multi-level tree");
        for (_, blob) in &packed.nodes {
            assert_eq!(blob.len(), 1228);
        }
    }

    /// A fanout of 1 must not be reachable: each level would be the same size as
    /// the one below, so the level walk would never reach a root and would grow
    /// until the process ran out of memory. A fill factor of 0, a negative one,
    /// or NaN all reduce to 1 without the floor.
    #[test]
    fn level_sizes_terminates_for_a_degenerate_fanout() {
        for per_node in [0, 1, 2] {
            let levels = level_sizes(1000, per_node);
            assert_eq!(
                levels.last(),
                Some(&1),
                "level walk did not reach a root for per_node {per_node}"
            );
            assert!(
                levels.len() <= 64,
                "level walk produced {} levels for per_node {per_node}",
                levels.len()
            );
        }
    }

    /// The fill factor changes how many entries land in each node, and every
    /// node still respects the format's capacity.
    #[test]
    fn fill_factor_controls_node_occupancy() {
        let entries: Vec<(i64, [f64; 4])> = (0..1000)
            .map(|i| (i64::from(i), [f64::from(i), f64::from(i), 0.0, 0.0]))
            .collect();

        let full = pack(&entries, 1228).unwrap();
        let mut half = Collected::default();
        pack_into(&entries, 1228, 0.5, &mut half).unwrap();

        // Capacity is (1228 - 4) / 24 = 51, so half fills 26 (25.5 rounded).
        let leaf_counts = |c: &Collected| -> Vec<usize> {
            let mut counts: Vec<usize> = c
                .nodes
                .iter()
                .map(|(_, blob)| decode_cells(blob).len())
                .collect();
            counts.sort_unstable();
            counts
        };
        assert_eq!(
            leaf_counts(&full).last(),
            Some(&51),
            "full packs to capacity"
        );
        assert_eq!(leaf_counts(&half).last(), Some(&26), "half fills half");
        assert!(
            half.nodes.len() > full.nodes.len(),
            "a lower fill factor should need more nodes"
        );

        // Both index every entry exactly once.
        for packed in [&full, &half] {
            let mut ids: Vec<i64> = packed.rowid_map.iter().map(|&(id, _)| id).collect();
            ids.sort_unstable();
            ids.dedup();
            assert_eq!(ids.len(), entries.len());
        }
    }

    /// A fill factor outside `(0, 1]` is clamped rather than producing an
    /// unusable tree: zero or negative would otherwise mean zero entries per
    /// node, and above one would overflow the node format.
    #[test]
    fn out_of_range_fill_factors_are_clamped() {
        let entries: Vec<(i64, [f64; 4])> = (0..200)
            .map(|i| (i64::from(i), [f64::from(i), f64::from(i), 0.0, 0.0]))
            .collect();

        for factor in [0.0, -1.0, 2.0, f64::NAN] {
            let mut collected = Collected::default();
            pack_into(&entries, 1228, factor, &mut collected).unwrap();
            for (_, blob) in &collected.nodes {
                let cells = decode_cells(blob).len();
                assert!(cells <= 51, "node over capacity with factor {factor}");
            }
            let mut ids: Vec<i64> = collected.rowid_map.iter().map(|&(id, _)| id).collect();
            ids.sort_unstable();
            ids.dedup();
            assert_eq!(
                ids.len(),
                entries.len(),
                "entries lost with factor {factor}"
            );
        }
    }

    /// An empty index still has a root node: a leaf at depth 0 with no cells.
    #[test]
    fn empty_entry_set_still_has_a_root() {
        let packed = pack(&[], 1228).unwrap();
        assert_eq!(packed.nodes.len(), 1);
        let (nodeno, blob) = packed.nodes.first().unwrap();
        assert_eq!(*nodeno, 1);
        assert_eq!(blob.len(), 1228);
        assert_eq!(u16::from_be_bytes([blob[0], blob[1]]), 0, "depth");
        assert_eq!(u16::from_be_bytes([blob[2], blob[3]]), 0, "cell count");
        assert!(packed.rowid_map.is_empty());
        assert!(packed.parent_map.is_empty());
    }

    /// A set small enough for one node produces a single root leaf, and every
    /// rowid maps to it.
    #[test]
    fn small_set_is_a_single_root_leaf() {
        let entries: Vec<(i64, [f64; 4])> = (1..=10)
            .map(|i| (i, [i as f64, i as f64, 0.0, 0.0]))
            .collect();
        let packed = pack(&entries, 1228).unwrap();
        assert_eq!(packed.nodes.len(), 1);
        assert_eq!(packed.nodes.first().unwrap().0, 1);
        assert!(packed.parent_map.is_empty());
        assert_eq!(packed.rowid_map.len(), 10);
        assert!(packed.rowid_map.iter().all(|&(_, nodeno)| nodeno == 1));
    }

    /// The root is node 1 and no node claims it as a child.
    #[test]
    fn root_is_node_one() {
        let entries: Vec<(i64, [f64; 4])> = (0..20_000)
            .map(|i| (i64::from(i), [f64::from(i), f64::from(i), 0.0, 0.0]))
            .collect();
        let packed = pack(&entries, 1228).unwrap();
        assert!(packed.nodes.iter().any(|(nodeno, _)| *nodeno == 1));
        assert!(
            packed.parent_map.iter().all(|&(child, _)| child != 1),
            "the root must not appear as a child"
        );
    }

    /// Minimum bounds round down and maxima round up, so a stored box always
    /// contains the true `f64` envelope.
    #[test]
    fn bounds_are_rounded_outward() {
        // A value with no exact f32 representation.
        let lo = 0.1_f64;
        let hi = 0.300_000_000_000_000_04_f64;
        assert!(f64::from(coord_down(lo)) <= lo);
        assert!(f64::from(coord_up(hi)) >= hi);

        // And across the whole packing path.
        let entries = vec![(1_i64, [lo, hi, -hi, -lo])];
        let packed = pack(&entries, 1228).unwrap();
        let cells = decode_cells(&packed.nodes.first().unwrap().1);
        let cell = cells.first().unwrap();
        assert!(f64::from(cell.bounds[0]) <= lo);
        assert!(f64::from(cell.bounds[1]) >= hi);
        assert!(f64::from(cell.bounds[2]) <= -hi);
        assert!(f64::from(cell.bounds[3]) >= -lo);
    }

    /// Every parent cell's bounds contain the bounds of the node it points at,
    /// which is the containment rule `rtreecheck` enforces.
    #[test]
    fn parent_bounds_contain_child_bounds() {
        let entries: Vec<(i64, [f64; 4])> = (0..30_000)
            .map(|i| {
                let x = f64::from(i % 173) * 1.7;
                let y = f64::from(i % 91) * -2.3;
                (i64::from(i), [x, x + 0.5, y, y + 0.5])
            })
            .collect();
        let packed = pack(&entries, 1228).unwrap();

        let bounds_of: std::collections::HashMap<i64, [f32; 4]> = packed
            .nodes
            .iter()
            .map(|(nodeno, blob)| {
                let cells = decode_cells(blob);
                let mut bounds = cells.first().map_or([0.0; 4], |c| c.bounds);
                for cell in &cells {
                    bounds = Cell::union(&bounds, &cell.bounds);
                }
                (*nodeno, bounds)
            })
            .collect();

        for (nodeno, blob) in &packed.nodes {
            // Only internal nodes have cells pointing at other nodes.
            if packed.parent_map.iter().any(|&(child, _)| child == *nodeno) || *nodeno == 1 {
                for cell in decode_cells(blob) {
                    if let Some(child) = bounds_of.get(&cell.id)
                        && packed
                            .parent_map
                            .iter()
                            .any(|&(c, p)| c == cell.id && p == *nodeno)
                    {
                        assert!(cell.bounds[0] <= child[0], "min_x not contained");
                        assert!(cell.bounds[1] >= child[1], "max_x not contained");
                        assert!(cell.bounds[2] <= child[2], "min_y not contained");
                        assert!(cell.bounds[3] >= child[3], "max_y not contained");
                    }
                }
            }
        }
    }

    /// Every entry appears exactly once in `%_rowid`, and every non-root node
    /// exactly once in `%_parent`: the counts `rtreecheck` compares against.
    #[test]
    fn mappings_cover_every_entry_and_node() {
        let entries: Vec<(i64, [f64; 4])> = (0..12_345)
            .map(|i| (i64::from(i), [f64::from(i), f64::from(i), 0.0, 0.0]))
            .collect();
        let packed = pack(&entries, 1228).unwrap();

        let mut ids: Vec<i64> = packed.rowid_map.iter().map(|&(id, _)| id).collect();
        ids.sort_unstable();
        ids.dedup();
        assert_eq!(ids.len(), entries.len(), "every rowid mapped exactly once");

        let mut children: Vec<i64> = packed.parent_map.iter().map(|&(c, _)| c).collect();
        children.sort_unstable();
        children.dedup();
        assert_eq!(
            children.len(),
            packed.nodes.len() - 1,
            "every non-root node has exactly one parent entry"
        );
    }
}