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Use Vec's binary search instead of hand-written one. #3021

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Merged
merged 2 commits into from
Aug 9, 2023
Merged

Use Vec's binary search instead of hand-written one. #3021

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Use Vec's binary search instead of hand-written one.
ttsugriy Aug 8, 2023
5b8057e
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RalfJung Aug 9, 2023
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23 changes: 6 additions & 17 deletions src/concurrency/range_object_map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,30 +42,19 @@ impl<T> RangeObjectMap<T> {
/// in an existing allocation, then returns Err containing the position
/// where such allocation should be inserted
fn find_offset(&self, offset: Size) -> Result<Position, Position> {
// We do a binary search.
let mut left = 0usize; // inclusive
let mut right = self.v.len(); // exclusive
loop {
if left == right {
// No element contains the given offset. But the
// position is where such element should be placed at.
return Err(left);
}
let candidate = left.checked_add(right).unwrap() / 2;
let elem = &self.v[candidate];
self.v.binary_search_by(|elem| -> std::cmp::Ordering {
if offset < elem.range.start {
// We are too far right (offset is further left).
debug_assert!(candidate < right); // we are making progress
right = candidate;
// (`Greater` means that `elem` is greater than the desired target.)
std::cmp::Ordering::Greater
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@RalfJung RalfJung Aug 9, 2023 •
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Please preserve the comments inside the ifs here, they still seem helpful.

Also have the comment explain that Greater indicates "elem is greater than desired target".

} else if offset >= elem.range.end() {
// We are too far left (offset is further right).
debug_assert!(candidate >= left); // we are making progress
left = candidate + 1;
std::cmp::Ordering::Less
} else {
// This is it!
return Ok(candidate);
std::cmp::Ordering::Equal
}
}
})
}

/// Determines whether a given access on `range` overlaps with
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