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index: extract inner binary search function

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The callback returns Ordering instead of &[u8] due to lifetime difficulty.
This commit is contained in:
Yuya Nishihara 2024-02-11 22:35:44 +09:00
parent 5b9f422d1d
commit 6fa660d9a8
1 changed files with 25 additions and 15 deletions
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40
lib/src/default_index/readonly.rs
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@ -373,21 +373,10 @@ impl ReadonlyIndexSegment {
/// Otherwise, returns `Err` containing the position where the id could be
/// inserted.
fn commit_id_byte_prefix_to_lookup_pos(&self, prefix: &[u8]) -> Result<u32, u32> {
let mut low = 0;
let mut high = self.num_local_commits;
while low < high {
let mid = (low + high) / 2;
let entry = self.commit_lookup_entry(mid);
let cmp = entry.commit_id_bytes().cmp(prefix);
// According to Rust std lib, this produces cmov instructions.
// https://github.com/rust-lang/rust/blob/1.76.0/library/core/src/slice/mod.rs#L2845-L2855
low = if cmp == Ordering::Less { mid + 1 } else { low };
high = if cmp == Ordering::Greater { mid } else { high };
if cmp == Ordering::Equal {
return Ok(mid);
}
}
Err(low)
binary_search_pos_by(self.num_local_commits, |pos| {
let entry = self.commit_lookup_entry(pos);
entry.commit_id_bytes().cmp(prefix)
})
}
}
@ -571,3 +560,24 @@ impl ReadonlyIndex for DefaultReadonlyIndex {
Box::new(DefaultMutableIndex::incremental(self.0.clone()))
}
}
/// Binary searches u32 position with the given comparison function.
///
/// If matched exactly, returns `Ok` with the position. Otherwise, returns `Err`
/// containing the position where the element could be inserted.
fn binary_search_pos_by(size: u32, mut f: impl FnMut(u32) -> Ordering) -> Result<u32, u32> {
let mut low = 0;
let mut high = size;
while low < high {
let mid = (low + high) / 2;
let cmp = f(mid);
// According to Rust std lib, this produces cmov instructions.
// https://github.com/rust-lang/rust/blob/1.76.0/library/core/src/slice/mod.rs#L2845-L2855
low = if cmp == Ordering::Less { mid + 1 } else { low };
high = if cmp == Ordering::Greater { mid } else { high };
if cmp == Ordering::Equal {
return Ok(mid);
}
}
Err(low)
}