1 files changed, 78 insertions, 0 deletions
diff --git a/src/mongo/util/lruishmap.h b/src/mongo/util/lruishmap.h
new file mode 100644
index 00000000000..ba91bf6f0f6
--- /dev/null
+++ b/src/mongo/util/lruishmap.h
@@ -0,0 +1,78 @@
+// lru-ish map.h
+
+/*    Copyright 2009 10gen Inc.
+ *
+ *    Licensed under the Apache License, Version 2.0 (the "License");
+ *    you may not use this file except in compliance with the License.
+ *    You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *    Unless required by applicable law or agreed to in writing, software
+ *    distributed under the License is distributed on an "AS IS" BASIS,
+ *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *    See the License for the specific language governing permissions and
+ *    limitations under the License.
+ */
+
+#pragma once
+
+#include "../pch.h"
+#include "../util/goodies.h"
+
+namespace mongo {
+
+    /* Your K object must define:
+         int hash() - must always return > 0.
+         operator==
+    */
+
+    template <class K, class V, int MaxChain>
+    class LRUishMap {
+    public:
+        LRUishMap(int _n) {
+            n = nextPrime(_n);
+            keys = new K[n];
+            hashes = new int[n];
+            for ( int i = 0; i < n; i++ ) hashes[i] = 0;
+        }
+        ~LRUishMap() {
+            delete[] keys;
+            delete[] hashes;
+        }
+
+        int _find(const K& k, bool& found) {
+            int h = k.hash();
+            assert( h > 0 );
+            int j = h % n;
+            int first = j;
+            for ( int i = 0; i < MaxChain; i++ ) {
+                if ( hashes[j] == h ) {
+                    if ( keys[j] == k ) {
+                        found = true;
+                        return j;
+                    }
+                }
+                else if ( hashes[j] == 0 ) {
+                    found = false;
+                    return j;
+                }
+            }
+            found = false;
+            return first;
+        }
+
+        V* find(const K& k) {
+            bool found;
+            int j = _find(k, found);
+            return found ? &values[j] : 0;
+        }
+
+    private:
+        int n;
+        K *keys;
+        int *hashes;
+        V *values;
+    };
+
+} // namespace mongo