const PolyphaseFilter *FindNearestPolyphaseFilter( int iUpFactor, float fCutoffFrequency )
{
/* Find a cached filter with the same iUpFactor and a nearby cutoff frequency.
* Round the cutoff down, if possible; it's better to filter out too much than
* too little. */
PolyphaseFiltersLock.Lock();
pair<int,float> params( make_pair(iUpFactor, fCutoffFrequency + 0.0001f) );
FilterMap::const_iterator it = g_mapPolyphaseFilters.upper_bound( params );
if( it != g_mapPolyphaseFilters.begin() )
--it;
ASSERT( it->first.first == iUpFactor );
PolyphaseFilter *pPolyphase = it->second;
PolyphaseFiltersLock.Unlock();
return pPolyphase;
}
