binaryurp/source/cache.hxx

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  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 != NULL);
  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         typedef std::pair<typename LruList::iterator, IdxType> MappedType;
  59         typedef std::pair<typename LruItMap::iterator,bool> MapPair;
  60         MapPair aMP = map_.insert( MappedType( list_.begin(), 0));
  61         *pbFound = !aMP.second;
  62
  63         if( !aMP.second) { // insertion not needed => found the entry
  64             list_.pop_front(); // remove the temp entry
  65             list_.splice( list_.begin(), list_, aMP.first->first); // the found entry is moved to front
  66             return aMP.first->second;
  67         }
  68
  69         // test insertion successful => it was new so we keep it
  70         IdxType n = static_cast<IdxType>( map_.size() - 1);
  71         if( n >= size_) { // cache full => replace the LRU entry
  72             // find the least recently used element in the map
  73             typename LruItMap::iterator it = map_.find( --list_.end());
  74             n = it->second;
  75             map_.erase( it); // remove it from the map
  76             list_.pop_back(); // remove from the list
  77         }
  78         aMP.first->second = n;
  79         return n;
  80     }
  81
  82 private:
  83     Cache(const Cache&) SAL_DELETED_FUNCTION;
  84     Cache& operator=(const Cache&) SAL_DELETED_FUNCTION;
  85
  86     typedef std::list<T> LruList; // last recently used list
  87     typedef typename LruList::iterator LruListIt;
  88     struct CmpT{ bool operator()( const LruListIt& rA, const LruListIt& rB) const { return (*rA<*rB);}};
  89     typedef ::std::map< LruListIt, IdxType, CmpT > LruItMap; // a map into a LruList
  90
  91     std::size_t size_;
  92     LruItMap map_;
  93     LruList list_;
  94 };
  95
  96 }
  97
  98 #endif
  99
 100 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */