Merge #61

61: Improve worst-case performance of HashSet.is_subset r=Amanieu a=Amanieu

Ported from rust-lang/rust#59665

Co-authored-by: Amanieu d'Antras <[email protected]>

Author: bors[bot]

src/external_trait_impls/rayon/set.rs

@@ -256,7 +256,11 @@ where
     ///
     /// This method runs in a potentially parallel fashion.
     pub fn par_is_subset(&self, other: &Self) -> bool {
-        self.into_par_iter().all(|x| other.contains(x))
+        if self.len() <= other.len() {
+            self.into_par_iter().all(|x| other.contains(x))
+        } else {
+            false
+        }
     }
 
     /// Returns `true` if the set is a superset of another,

src/raw/mod.rs

@@ -145,7 +145,7 @@ fn h2(hash: u64) -> u8 {
 /// (skipping over 1 group), then 3 groups (skipping over 2 groups), and so on.
 ///
 /// Proof that the probe will visit every group in the table:
-/// https://fgiesen.wordpress.com/2015/02/22/triangular-numbers-mod-2n/
+/// <https://fgiesen.wordpress.com/2015/02/22/triangular-numbers-mod-2n/>
 struct ProbeSeq {
     bucket_mask: usize,
     pos: usize,
@@ -935,12 +935,12 @@ impl<T> RawTable<T> {
     /// should be dropped using a `RawIter` before freeing the allocation.
     #[inline]
     pub fn into_alloc(self) -> Option<(NonNull<u8>, Layout)> {
-        let alloc = if !self.is_empty_singleton() {
+        let alloc = if self.is_empty_singleton() {
+            None
+        } else {
             let (layout, _) = calculate_layout::<T>(self.buckets())
                 .unwrap_or_else(|| unsafe { hint::unreachable_unchecked() });
             Some((self.ctrl.cast(), layout))
-        } else {
-            None
         };
         mem::forget(self);
         alloc

src/set.rs

@@ -640,7 +640,11 @@ where
     /// assert_eq!(set.is_subset(&sup), false);
     /// ```
     pub fn is_subset(&self, other: &Self) -> bool {
-        self.iter().all(|v| other.contains(v))
+        if self.len() <= other.len() {
+            self.iter().all(|v| other.contains(v))
+        } else {
+            false
+        }
     }
 
     /// Returns `true` if the set is a superset of another,