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[rustc_data_structures] Use partition_point to find binary_search_slice end.

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This commit is contained in:
Taras Tsugrii 2023-07-29 19:42:22 -07:00
parent fb53384c94
commit 9ced089569
1 changed files with 8 additions and 21 deletions
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29
compiler/rustc_data_structures/src/binary_search_util/mod.rs
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@ -14,31 +14,18 @@ pub fn binary_search_slice<'d, E, K>(data: &'d [E], key_fn: impl Fn(&E) -> K, ke
let start = data.partition_point(|x| key_fn(x) < *key);
// At this point `start` either points at the first entry with equal or
// greater key or is equal to `size` in case all elements have smaller keys
// Invariant: start == size || key_fn(&data[start]) >= *key
if start == size || key_fn(&data[start]) != *key {
return &[];
};
// Invariant: start < size && key_fn(&data[start]) == *key
// Now search forward to find the *last* one.
let mut end = start;
let mut previous = start;
let mut step = 1;
loop {
end = end.saturating_add(step).min(size);
if end == size || key_fn(&data[end]) != *key {
break;
}
previous = end;
step *= 2;
}
step = end - previous;
while step > 1 {
let half = step / 2;
let mid = end - half;
if key_fn(&data[mid]) != *key {
end = mid;
}
step -= half;
}
// Find the first entry with key > `key`. Skip `start` entries since
// key_fn(&data[start]) == *key
// Invariant: offset == size || key_fn(&data[offset]) >= *key
let offset = start + 1;
let end = data[offset..].partition_point(|x| key_fn(x) <= *key) + offset;
// Invariant: end == size || key_fn(&data[end]) > *key
&data[start..end]
}