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469ca379d6
This introduces a no-op `Unhasher` for map keys that are already hash- like, for example `Fingerprint` and its wrapper `DefPathHash`. For these we can directly produce the `u64` hash for maps. The first use of this is `def_path_hash_to_def_id: Option<UnhashMap<DefPathHash, DefId>>`.
30 lines
788 B
Rust
30 lines
788 B
Rust
use std::collections::{HashMap, HashSet};
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use std::hash::{BuildHasherDefault, Hasher};
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pub type UnhashMap<K, V> = HashMap<K, V, BuildHasherDefault<Unhasher>>;
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pub type UnhashSet<V> = HashSet<V, BuildHasherDefault<Unhasher>>;
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/// This no-op hasher expects only a single `write_u64` call. It's intended for
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/// map keys that already have hash-like quality, like `Fingerprint`.
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#[derive(Default)]
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pub struct Unhasher {
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value: u64,
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}
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impl Hasher for Unhasher {
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#[inline]
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fn finish(&self) -> u64 {
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self.value
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}
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fn write(&mut self, _bytes: &[u8]) {
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unimplemented!("use write_u64");
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}
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#[inline]
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fn write_u64(&mut self, value: u64) {
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debug_assert_eq!(0, self.value, "Unhasher doesn't mix values!");
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self.value = value;
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}
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}
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