C++ High Performance

Evaluating get_bitmap_resource() with PrehashedString

Let's return to our original get_bitmap_resource() function, the std::string originally used is exchanged to a PrehashedString:

// Bitmap cache 
auto get_bitmap_resource(const PrehashedString& path) -> const Bitmap& { 
  // Static storage of all loaded bitmaps 
  static auto loaded_bitmaps =     std::unordered_map<PrehashedString, Bitmap>{}; 
  // If the bitmap is already in loaded_bitmaps, return it 
  if (loaded_bitmaps.count(path) > 0) { 
    return loaded_bitmaps.at(path).second; 
  } 
  // The bitmap isn't already loaded, load and return it 
  auto bitmap = load_bitmap_from_filesystem(path.c_str()); 
  loaded_bitmaps.emplace(path, std::move(bitmap)); 
  return loaded_bitmaps.at(path); 
} 

We also need a function ...