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Prefer partition_point to look up assoc items

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Yuki Okushi 2021-06-17 11:40:37 +09:00
parent 9fef8d91b4
commit c0efd2a15b
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1 changed files with 5 additions and 47 deletions
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52
compiler/rustc_data_structures/src/sorted_map/index_map.rs
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@ -94,13 +94,15 @@ impl<I: Idx, K: Ord, V> SortedIndexMultiMap<I, K, V> {
Q: Ord + ?Sized,
K: Borrow<Q>,
{
// FIXME: This should be in the standard library as `equal_range`. See rust-lang/rfcs#2184.
match self.binary_search_idx(key) {
Err(_) => self.idxs_to_items_enumerated(&[]),
Ok(idx) => {
let start = self.find_lower_bound(key, idx);
let end = self.find_upper_bound(key, idx);
let start = self.idx_sorted_by_item_key[..idx]
.partition_point(|&i| self.items[i].0.borrow() != key);
let end = idx
+ self.idx_sorted_by_item_key[idx..]
.partition_point(|&i| self.items[i].0.borrow() == key);
self.idxs_to_items_enumerated(&self.idx_sorted_by_item_key[start..end])
}
}
@ -114,50 +116,6 @@ impl<I: Idx, K: Ord, V> SortedIndexMultiMap<I, K, V> {
self.idx_sorted_by_item_key.binary_search_by(|&idx| self.items[idx].0.borrow().cmp(key))
}
/// Returns the index into the `idx_sorted_by_item_key` array of the first item equal to
/// `key`.
///
/// `initial` must be an index into that same array for an item that is equal to `key`.
fn find_lower_bound<Q>(&self, key: &Q, initial: usize) -> usize
where
Q: Ord + ?Sized,
K: Borrow<Q>,
{
debug_assert!(self.items[self.idx_sorted_by_item_key[initial]].0.borrow() == key);
// FIXME: At present, this uses linear search, meaning lookup is only `O(log n)` if duplicate
// entries are rare. It would be better to start with a linear search for the common case but
// fall back to an exponential search if many duplicates are found. This applies to
// `upper_bound` as well.
let mut start = initial;
while start != 0 && self.items[self.idx_sorted_by_item_key[start - 1]].0.borrow() == key {
start -= 1;
}
start
}
/// Returns the index into the `idx_sorted_by_item_key` array of the first item greater than
/// `key`, or `self.len()` if no such item exists.
///
/// `initial` must be an index into that same array for an item that is equal to `key`.
fn find_upper_bound<Q>(&self, key: &Q, initial: usize) -> usize
where
Q: Ord + ?Sized,
K: Borrow<Q>,
{
debug_assert!(self.items[self.idx_sorted_by_item_key[initial]].0.borrow() == key);
// See the FIXME for `find_lower_bound`.
let mut end = initial + 1;
let len = self.items.len();
while end < len && self.items[self.idx_sorted_by_item_key[end]].0.borrow() == key {
end += 1;
}
end
}
fn idxs_to_items_enumerated(&'a self, idxs: &'a [I]) -> impl 'a + Iterator<Item = (I, &'a V)> {
idxs.iter().map(move |&idx| (idx, &self.items[idx].1))
}