binaryurp/source/cache.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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   9  * This file incorporates work covered by the following license notice:
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  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 #ifndef INCLUDED_BINARYURP_SOURCE_CACHE_HXX
  21 #define INCLUDED_BINARYURP_SOURCE_CACHE_HXX
  22
  23 #include <sal/config.h>
  24
  25 #include <cassert>
  26 #include <cstddef>
  27 #include <map>
  28 #include <list>
  29
  30 #include <sal/types.h>
  31
  32 namespace binaryurp {
  33
  34 namespace cache {
  35
  36 enum { size = 256, ignore = 0xFFFF };
  37
  38 }
  39
  40 template< typename T > class Cache {
  41 public:
  42     typedef sal_uInt16 IdxType;
  43
  44     explicit Cache(std::size_t size):
  45         size_(size)
  46     {
  47         assert(size < cache::ignore);
  48     }
  49
  50     IdxType add( const T& rContent, bool* pbFound) {
  51         assert( pbFound != nullptr);
  52         if( !size_) {
  53             *pbFound = false;
  54             return cache::ignore;
  55         }
  56         // try to insert into the map
  57         list_.push_front( rContent); // create a temp entry
  58         auto const [it, inserted] = map_.emplace( list_.begin(), 0 );
  59         *pbFound = !inserted;
  60
  61         if( !inserted) { // insertion not needed => found the entry
  62             list_.pop_front(); // remove the temp entry
  63             list_.splice( list_.begin(), list_, it->first); // the found entry is moved to front
  64             return it->second;
  65         }
  66
  67         // test insertion successful => it was new so we keep it
  68         IdxType n = static_cast<IdxType>( map_.size() - 1);
  69         if( n >= size_) { // cache full => replace the LRU entry
  70             // find the least recently used element in the map
  71             typename LruItMap::iterator lru = map_.find( --list_.end());
  72             n = lru->second;
  73             map_.erase( lru); // remove it from the map
  74             list_.pop_back(); // remove from the list
  75         }
  76         it->second = n;
  77         return n;
  78     }
  79
  80 private:
  81     Cache(const Cache&) = delete;
  82     Cache& operator=(const Cache&) = delete;
  83
  84     typedef std::list<T> LruList; // last recently used list
  85     typedef typename LruList::iterator LruListIt;
  86     struct CmpT{ bool operator()( const LruListIt& rA, const LruListIt& rB) const { return (*rA<*rB);}};
  87     typedef std::map< LruListIt, IdxType, CmpT > LruItMap; // a map into a LruList
  88
  89     std::size_t size_;
  90     LruItMap map_;
  91     LruList list_;
  92 };
  93
  94 }
  95
  96 #endif
  97
  98 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */