binaryurp/source/cache.hxx

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  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 "boost/noncopyable.hpp"
  31 #include "sal/types.h"
  32
  33 namespace binaryurp {
  34
  35 namespace cache {
  36
  37 enum { size = 256, ignore = 0xFFFF };
  38
  39 }
  40
  41 template< typename T > class Cache : private boost::noncopyable {
  42 public:
  43     typedef sal_uInt16 IdxType;
  44
  45     explicit Cache(std::size_t size):
  46         size_(size)
  47     {
  48         assert(size < cache::ignore);
  49     }
  50
  51     IdxType add( const T& rContent, bool* pbFound) {
  52         assert( pbFound != NULL);
  53         if( !size_) {
  54                 *pbFound = false;
  55                 return cache::ignore;
  56         }
  57         // try to insert into the map
  58         list_.push_front( rContent); // create a temp entry
  59         typedef std::pair<typename LruList::iterator, IdxType> MappedType;
  60         typedef std::pair<typename LruItMap::iterator,bool> MapPair;
  61         MapPair aMP = map_.insert( MappedType( list_.begin(), 0));
  62         *pbFound = !aMP.second;
  63
  64         if( !aMP.second) { // insertion not needed => found the entry
  65                 list_.pop_front(); // remove the temp entry
  66                 list_.splice( list_.begin(), list_, aMP.first->first); // the found entry is moved to front
  67                 return aMP.first->second;
  68         }
  69
  70         // test insertion successful => it was new so we keep it
  71         IdxType n = static_cast<IdxType>( map_.size() - 1);
  72         if( n >= size_) { // cache full => replace the LRU entry
  73                 // find the least recently used element in the map
  74                 typename LruItMap::iterator it = map_.find( --list_.end());
  75                 n = it->second;
  76                 map_.erase( it); // remove it from the map
  77                 list_.pop_back(); // remove from the list
  78         }
  79         aMP.first->second = n;
  80         return n;
  81     }
  82
  83 private:
  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: */