1 files changed, 95 insertions, 0 deletions
diff --git a/binaryurp/source/cache.hxx b/binaryurp/source/cache.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you 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 .
+ */
+
+#pragma once
+
+#include <sal/config.h>
+
+#include <cassert>
+#include <cstddef>
+#include <map>
+#include <list>
+
+#include <sal/types.h>
+
+namespace binaryurp {
+
+namespace cache {
+
+enum { size = 256, ignore = 0xFFFF };
+
+}
+
+template< typename T > class Cache {
+public:
+    typedef sal_uInt16 IdxType;
+
+    explicit Cache(std::size_t size):
+        size_(size)
+    {
+        assert(size < cache::ignore);
+    }
+
+    IdxType add( const T& rContent, bool* pbFound) {
+        assert( pbFound != nullptr);
+        if( !size_) {
+            *pbFound = false;
+            return cache::ignore;
+        }
+        // try to insert into the map
+        list_.push_front( rContent); // create a temp entry
+        auto const [it, inserted] = map_.emplace( list_.begin(), 0 );
+        *pbFound = !inserted;
+
+        if( !inserted) { // insertion not needed => found the entry
+            list_.pop_front(); // remove the temp entry
+            list_.splice( list_.begin(), list_, it->first); // the found entry is moved to front
+            return it->second;
+        }
+
+        // test insertion successful => it was new so we keep it
+        IdxType n = static_cast<IdxType>( map_.size() - 1);
+        if( n >= size_) { // cache full => replace the LRU entry
+            // find the least recently used element in the map
+            typename LruItMap::iterator lru = map_.find( --list_.end());
+            n = lru->second;
+            map_.erase( lru); // remove it from the map
+            list_.pop_back(); // remove from the list
+        }
+        it->second = n;
+        return n;
+    }
+
+private:
+    Cache(const Cache&) = delete;
+    Cache& operator=(const Cache&) = delete;
+
+    typedef std::list<T> LruList; // last recently used list
+    typedef typename LruList::iterator LruListIt;
+    struct CmpT{ bool operator()( const LruListIt& rA, const LruListIt& rB) const { return (*rA<*rB);}};
+    typedef std::map< LruListIt, IdxType, CmpT > LruItMap; // a map into a LruList
+
+    std::size_t size_;
+    LruItMap map_;
+    LruList list_;
+};
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */