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Document how the HashN types are different from Fingerprint

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This commit is contained in:
Ben Kimock 2023-04-15 14:58:50 -04:00
parent 0445fbdd83
commit a04c09ade8
1 changed files with 15 additions and 4 deletions
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19
compiler/rustc_data_structures/src/hashes.rs
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@ -1,7 +1,20 @@
//! rustc encodes a lot of hashes. If hashes are stored as `u64` or `u128`, a `derive(Encodable)`
//! will apply varint encoding to the hashes, which is less efficient than directly encoding the 8
//! or 16 bytes of the hash.
//!
//! The types in this module represent 64-bit or 128-bit hashes produced by a `StableHasher`.
//! `Hash64` and `Hash128` expose some utilty functions to encourage users to not extract the inner
//! hash value as an integer type and accidentally apply varint encoding to it.
//!
//! In contrast with `Fingerprint`, users of these types cannot and should not attempt to construct
//! and decompose these types into constitutent pieces. The point of these types is only to
//! connect the fact that they can only be produced by a `StableHasher` to their
//! `Encode`/`Decode` impls.
use crate::stable_hasher::{StableHasher, StableHasherResult};
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use std::fmt;
use std::ops::BitXorAssign;
use crate::stable_hasher::{StableHasher, StableHasherResult};
#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
pub struct Hash64 {
@ -74,9 +87,7 @@ impl Hash128 {
#[inline]
pub fn wrapping_add(self, other: Self) -> Self {
Self {
inner: self.inner.wrapping_add(other.inner),
}
Self { inner: self.inner.wrapping_add(other.inner) }
}
#[inline]