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Fix off-by-one that corrupts a bitmap in remove_smallest/remove_biggest (#359) #363

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Merged
Kerollmops merged 1 commit into from
Aug 12, 2026
Merged

Fix off-by-one that corrupts a bitmap in remove_smallest/remove_biggest (#359) #363

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36 changes: 34 additions & 2 deletions roaring/src/bitmap/store/interval_store.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -261,7 +261,10 @@ impl IntervalStore {
}
}
if let Some(last_interval) = last_interval {
if last_interval.run_len() < amount {
// `<=`, not `<`: when the amount left equals this interval's run
// length the whole interval is consumed and must be dropped, not
// shrunk to `start = end + 1` (an inverted interval) (#359).
if last_interval.run_len() <= amount {
remove_to += 1;
} else {
last_interval.start += amount as u16;
Expand All @@ -285,7 +288,11 @@ impl IntervalStore {
}
}
if let Some(last_interval) = last_interval {
if last_interval.run_len() >= amount {
// `>`, not `>=`: when the amount left equals this interval's run
// length the whole interval is consumed and is removed by the
// `drain` below; shrinking it would set `end = start - 1` (an
// inverted interval) (#359).
if last_interval.run_len() > amount {
remove_to += 1;
last_interval.end -= amount as u16;
}
Expand Down Expand Up @@ -1657,6 +1664,31 @@ mod tests {
assert_eq!(interval_store, IntervalStore(alloc::vec![Interval::new_unchecked(1, 5800),]));
}

#[test]
fn remove_smallest_exact_interval_boundary() {
// #359: removing exactly the run length of the first interval must drop
// it entirely, not shrink it past its end into an inverted interval.
let mut interval_store = IntervalStore(alloc::vec![
Interval { start: 0, end: 2 },
Interval { start: 4, end: 4 },
]);
interval_store.remove_smallest(3); // == run_len of [0, 2]
assert_eq!(interval_store, IntervalStore(alloc::vec![Interval::new_unchecked(4, 4)]));
}

#[test]
fn remove_biggest_exact_interval_boundary() {
// #359: removing exactly the run length of the last interval must drop
// it entirely, not shrink its end below its start into an inverted
// interval.
let mut interval_store = IntervalStore(alloc::vec![
Interval { start: 2, end: 2 },
Interval { start: 4, end: 8 },
]);
interval_store.remove_biggest(5); // == run_len of [4, 8]
assert_eq!(interval_store, IntervalStore(alloc::vec![Interval::new_unchecked(2, 2)]));
}

#[test]
fn contains_index_1() {
let interval_store = IntervalStore(alloc::vec![
Expand Down
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