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copied!<p>I just wanted to post a helpful article about bitArrays for those of us who are developing our own versions of Faceting with Lucene.net. See: <a href="http://dotnetperls.com/precomputed-bitcount" rel="nofollow noreferrer">http://dotnetperls.com/precomputed-bitcount</a> </p> <p>This is a good explination on the fastet way to get the cardinality of the on bits in an integer ( which is a bulk of what the above code sample does ).</p> <p>Imlementing the method in the article in my faceted search and some other simple changes i was able to cut the time it took the get the count by ~ 65%. The differences where in:</p> <ol> <li>Declaring the _bitcount global ( so its not created per call )</li> <li>Changing the for to foreach (ANT Profiler showed a 25% gain here)</li> <li><p>Implementening the 65535 table vs the 256 to shift 16 bits at a time rather then 8.</p> <pre><code>private static int[] _bitcounts = InitializeBitcounts(); private static int GetCardinality(BitArray bitArray) { uint[] array = (uint[])bitArray.GetType().GetField("m_array", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(bitArray); int count = 0; foreach (uint value in array) { count += _bitcounts[value & 65535] + _bitcounts[(value >> 16) & 65535]; } return count; } private static int[] InitializeBitcounts() { int[] bitcounts = new int[65536]; int position1 = -1; int position2 = -1; // // Loop through all the elements and assign them. // for (int i = 1; i < 65536; i++, position1++) { // // Adjust the positions we read from. // if (position1 == position2) { position1 = 0; position2 = i; } bitcounts[i] = bitcounts[position1] + 1; } return bitcounts; } </code></pre></li> </ol>

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