perf: use regular mul instead of checked_mul when doubling capacity

bluurryy · Oct 29, 2024 · 6cb6d1b · 6cb6d1b
1 parent ae0c8eb
commit 6cb6d1b
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Showing 3 changed files with 9 additions and 6 deletions.
diff --git a/src/bump_vec.rs b/src/bump_vec.rs
@@ -1616,8 +1616,9 @@ where
             return Ok(());
         }
 
-        let new_cap = self.capacity().checked_mul(2).unwrap_or(required_cap).max(required_cap);
-        let new_cap = new_cap.max(min_non_zero_cap(T::SIZE));
+        // This guarantees exponential growth. The doubling cannot overflow
+        // because `capacity <= isize::MAX` and the type of `capacity` is usize;
+        let new_cap = (self.capacity() * 2).max(required_cap).max(min_non_zero_cap(T::SIZE));
 
         self.generic_grow_to(new_cap)
     }

diff --git a/src/mut_bump_vec.rs b/src/mut_bump_vec.rs
@@ -1309,8 +1309,9 @@ where
             return Ok(());
         }
 
-        let new_cap = self.capacity().checked_mul(2).unwrap_or(required_cap).max(required_cap);
-        let new_cap = new_cap.max(min_non_zero_cap(T::SIZE));
+        // This guarantees exponential growth. The doubling cannot overflow
+        // because `capacity <= isize::MAX` and the type of `capacity` is usize;
+        let new_cap = (self.capacity() * 2).max(required_cap).max(min_non_zero_cap(T::SIZE));
 
         unsafe { self.generic_grow_to(new_cap) }
     }

diff --git a/src/mut_bump_vec_rev.rs b/src/mut_bump_vec_rev.rs
@@ -1334,8 +1334,9 @@ where
             return Ok(());
         }
 
-        let new_cap = self.capacity().checked_mul(2).unwrap_or(required_cap).max(required_cap);
-        let new_cap = new_cap.max(min_non_zero_cap(T::SIZE));
+        // This guarantees exponential growth. The doubling cannot overflow
+        // because `capacity <= isize::MAX` and the type of `capacity` is usize;
+        let new_cap = (self.capacity() * 2).max(required_cap).max(min_non_zero_cap(T::SIZE));
 
         unsafe { self.generic_grow_to(new_cap) }
     }