diff options
| -rw-r--r-- | compiler/rustc_data_structures/src/hashes.rs | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/compiler/rustc_data_structures/src/hashes.rs b/compiler/rustc_data_structures/src/hashes.rs index 9f6e0fb7676..f32f6912267 100644 --- a/compiler/rustc_data_structures/src/hashes.rs +++ b/compiler/rustc_data_structures/src/hashes.rs @@ -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] |