Use full hash bytes and use fixed endianness

rust-lang · Jul 15, 2024 · 311050d · 311050d
1 parent 38b97bc
commit 311050d
Show file tree

Hide file tree

Showing 2 changed files with 35 additions and 7 deletions.
diff --git a/compiler/rustc_data_structures/src/fingerprint.rs b/compiler/rustc_data_structures/src/fingerprint.rs
@@ -159,11 +159,16 @@ impl FromStableHash for Fingerprint {
 
     #[inline]
     fn from(hash: Self::Hash) -> Self {
-        let bytes = hash.as_bytes();
-        Fingerprint(
-            u64::from_ne_bytes(bytes[0..8].try_into().unwrap()),
-            u64::from_ne_bytes(bytes[8..16].try_into().unwrap()),
-        )
+        let bytes: &[u8; 32] = hash.as_bytes();
+
+        let p0 = u64::from_le_bytes(bytes[0..8].try_into().unwrap());
+        let p1 = u64::from_le_bytes(bytes[8..16].try_into().unwrap());
+        let p2 = u64::from_le_bytes(bytes[16..24].try_into().unwrap());
+        let p3 = u64::from_le_bytes(bytes[24..32].try_into().unwrap());
+
+        // See https://stackoverflow.com/a/27952689 on why this function is
+        // implemented this way.
+        Fingerprint(p0.wrapping_mul(3).wrapping_add(p1), p2.wrapping_mul(3).wrapping_add(p3))
     }
 }
 

diff --git a/compiler/rustc_data_structures/src/hashes.rs b/compiler/rustc_data_structures/src/hashes.rs
@@ -62,7 +62,19 @@ impl FromStableHash for Hash64 {
     #[inline]
     fn from(hash: Self::Hash) -> Self {
         let bytes = hash.as_bytes();
-        Self { inner: u64::from_ne_bytes(bytes[0..8].try_into().unwrap()) }
+
+        let p0 = u64::from_le_bytes(bytes[0..8].try_into().unwrap());
+        let p1 = u64::from_le_bytes(bytes[8..16].try_into().unwrap());
+        let p2 = u64::from_le_bytes(bytes[16..24].try_into().unwrap());
+        let p3 = u64::from_le_bytes(bytes[24..32].try_into().unwrap());
+
+        // See https://stackoverflow.com/a/27952689 on why this function is
+        // implemented this way.
+        let m0 = p0.wrapping_mul(3).wrapping_add(p1);
+        let m1 = p2.wrapping_mul(3).wrapping_add(p3);
+        let h = m0.wrapping_mul(3).wrapping_add(m1);
+
+        Self { inner: h }
     }
 }
 
@@ -130,7 +142,18 @@ impl FromStableHash for Hash128 {
     #[inline]
     fn from(hash: Self::Hash) -> Self {
         let bytes = hash.as_bytes();
-        Self { inner: u128::from_ne_bytes(bytes[0..16].try_into().unwrap()) }
+
+        let p0 = u64::from_le_bytes(bytes[0..8].try_into().unwrap());
+        let p1 = u64::from_le_bytes(bytes[8..16].try_into().unwrap());
+        let p2 = u64::from_le_bytes(bytes[16..24].try_into().unwrap());
+        let p3 = u64::from_le_bytes(bytes[24..32].try_into().unwrap());
+
+        // See https://stackoverflow.com/a/27952689 on why this function is
+        // implemented this way.
+        let upper = p0.wrapping_mul(3).wrapping_add(p1);
+        let lower = p2.wrapping_mul(3).wrapping_add(p3);
+
+        Self { inner: u128::from(lower) | (u128::from(upper) << 64) }
     }
 }