add reserve_at_least method to LinearMap/LinearSet

Author: thestinger

src/libcore/hashmap.rs

@@ -51,6 +51,7 @@ pub mod linear {
         FoundEntry(uint), FoundHole(uint), TableFull
     }
 
+    #[inline(always)]
     pure fn resize_at(capacity: uint) -> uint {
         ((capacity as float) * 3. / 4.) as uint
     }
@@ -126,12 +127,19 @@ pub mod linear {
             TableFull
         }
 
-        /// Expands the capacity of the array and re-inserts each
-        /// of the existing buckets.
+        /// Expand the capacity of the array to the next power of two
+        /// and re-insert each of the existing buckets.
+        #[inline(always)]
         fn expand(&mut self) {
+            let new_capacity = self.buckets.len() * 2;
+            self.resize(new_capacity);
+        }
+
+        /// Expands the capacity of the array and re-insert each of the
+        /// existing buckets.
+        fn resize(&mut self, new_capacity: uint) {
             let old_capacity = self.buckets.len();
-            let new_capacity = old_capacity * 2;
-            self.resize_at = ((new_capacity as float) * 3.0 / 4.0) as uint;
+            self.resize_at = resize_at(new_capacity);
 
             let mut old_buckets = vec::from_fn(new_capacity, |_| None);
             self.buckets <-> old_buckets;
@@ -331,6 +339,14 @@ pub mod linear {
             linear_map_with_capacity(INITIAL_CAPACITY)
         }
 
+        /// Reserve space for at least `n` elements in the hash table.
+        fn reserve_at_least(&mut self, n: uint) {
+            if n > self.buckets.len() {
+                let buckets = n * 4 / 3 + 1;
+                self.resize(uint::next_power_of_two(buckets));
+            }
+        }
+
         fn pop(&mut self, k: &K) -> Option<V> {
             let hash = k.hash_keyed(self.k0, self.k1) as uint;
             self.pop_internal(hash, k)
@@ -562,6 +578,11 @@ pub mod linear {
     pub impl <T: Hash IterBytes Eq> LinearSet<T> {
         /// Create an empty LinearSet
         static fn new() -> LinearSet<T> { LinearSet{map: LinearMap::new()} }
+
+        /// Reserve space for at least `n` elements in the hash table.
+        fn reserve_at_least(&mut self, n: uint) {
+            self.map.reserve_at_least(n)
+        }
     }
 }