1 files changed, 132 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/hashes.rs b/compiler/rustc_data_structures/src/hashes.rs
new file mode 100644
index 000000000..ad068cdbc
--- /dev/null
+++ b/compiler/rustc_data_structures/src/hashes.rs
@@ -0,0 +1,132 @@
+//! 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;
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
+pub struct Hash64 {
+    inner: u64,
+}
+
+impl Hash64 {
+    pub const ZERO: Hash64 = Hash64 { inner: 0 };
+
+    #[inline]
+    pub(crate) fn new(n: u64) -> Self {
+        Self { inner: n }
+    }
+
+    #[inline]
+    pub fn as_u64(self) -> u64 {
+        self.inner
+    }
+}
+
+impl BitXorAssign<u64> for Hash64 {
+    #[inline]
+    fn bitxor_assign(&mut self, rhs: u64) {
+        self.inner ^= rhs;
+    }
+}
+
+impl<S: Encoder> Encodable<S> for Hash64 {
+    #[inline]
+    fn encode(&self, s: &mut S) {
+        s.emit_raw_bytes(&self.inner.to_le_bytes());
+    }
+}
+
+impl<D: Decoder> Decodable<D> for Hash64 {
+    #[inline]
+    fn decode(d: &mut D) -> Self {
+        Self { inner: u64::from_le_bytes(d.read_raw_bytes(8).try_into().unwrap()) }
+    }
+}
+
+impl StableHasherResult for Hash64 {
+    #[inline]
+    fn finish(hasher: StableHasher) -> Self {
+        Self { inner: hasher.finalize().0 }
+    }
+}
+
+impl fmt::Debug for Hash64 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::LowerHex for Hash64 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.inner, f)
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
+pub struct Hash128 {
+    inner: u128,
+}
+
+impl Hash128 {
+    #[inline]
+    pub fn truncate(self) -> Hash64 {
+        Hash64 { inner: self.inner as u64 }
+    }
+
+    #[inline]
+    pub fn wrapping_add(self, other: Self) -> Self {
+        Self { inner: self.inner.wrapping_add(other.inner) }
+    }
+
+    #[inline]
+    pub fn as_u128(self) -> u128 {
+        self.inner
+    }
+}
+
+impl<S: Encoder> Encodable<S> for Hash128 {
+    #[inline]
+    fn encode(&self, s: &mut S) {
+        s.emit_raw_bytes(&self.inner.to_le_bytes());
+    }
+}
+
+impl<D: Decoder> Decodable<D> for Hash128 {
+    #[inline]
+    fn decode(d: &mut D) -> Self {
+        Self { inner: u128::from_le_bytes(d.read_raw_bytes(16).try_into().unwrap()) }
+    }
+}
+
+impl StableHasherResult for Hash128 {
+    #[inline]
+    fn finish(hasher: StableHasher) -> Self {
+        let (_0, _1) = hasher.finalize();
+        Self { inner: u128::from(_0) | (u128::from(_1) << 64) }
+    }
+}
+
+impl fmt::Debug for Hash128 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::LowerHex for Hash128 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.inner, f)
+    }
+}