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Add special case for length 1

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Jakub Beránek 2021-12-13 21:34:54 +01:00
parent ac08f13948
commit 1f284b07ed
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1 changed files with 17 additions and 9 deletions
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26
compiler/rustc_data_structures/src/stable_hasher.rs
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@ -559,20 +559,28 @@ where
fn stable_hash_reduce<HCX, I, C, F>(
hcx: &mut HCX,
hasher: &mut StableHasher,
collection: C,
mut collection: C,
length: usize,
hash_function: F,
) where
C: Iterator<Item = I>,
F: Fn(&mut StableHasher, &mut HCX, I),
{
let hash = collection
.map(|value| {
let mut hasher = StableHasher::new();
hash_function(&mut hasher, hcx, value);
hasher.finish::<u128>()
})
.reduce(|accum, value| accum.wrapping_add(value));
length.hash_stable(hcx, hasher);
hash.hash_stable(hcx, hasher);
match length {
1 => {
hash_function(hasher, hcx, collection.next().unwrap());
}
_ => {
let hash = collection
.map(|value| {
let mut hasher = StableHasher::new();
hash_function(&mut hasher, hcx, value);
hasher.finish::<u128>()
})
.reduce(|accum, value| accum.wrapping_add(value));
hash.hash_stable(hcx, hasher);
}
}
}