C:/Users/Andreas Schiffler/Desktop/SVN/NewGamePhysics/NewGamePhysics/Utilities/BitCount.cs

//-----------------------------------------------------------------------------
// BitCount.cs
// (A. Schiffler, 2009)
//-----------------------------------------------------------------------------

namespace NewGamePhysics.Utilities
{
    using System;

    class BitCount
    {
        static byte[] bitcountCache;

        public BitCount()
        {
            // Initialize cache
            bitcountCache = new byte[65536];
            for (int i = 0; i < 65536; i++)
            {
                bitcountCache[i] = SparseBitcount(i);
            }
        }

        public int FastBitcount(ushort testThis)
        {
            return bitcountCache[testThis];
        }

        public int FastBitcount(short testThis)
        {
            return FastBitcount((ushort)testThis);
        }

        public int FastBitcount(uint testThis)
        {
            return bitcountCache[(testThis >> (0 * 16)) & 65535] +
                   bitcountCache[(testThis >> (1 * 16)) & 65535];
        }

        public int FastBitcount(int testThis)
        {
            return FastBitcount((uint)testThis);
        }

        public int FastBitcount(ulong testThis)
        {
            return bitcountCache[(testThis >> (0 * 16)) & 65535L] +
                   bitcountCache[(testThis >> (1 * 16)) & 65535L] +
                   bitcountCache[(testThis >> (2 * 16)) & 65535L] +
                   bitcountCache[(testThis >> (3 * 16)) & 65535L];
        }

        public int FastBitcount(long testThis)
        {
            return FastBitcount((ulong)testThis);
        }

        public int FastBitcount(double testThis)
        {
            // Translate the double into a 64 bit long.
            long testThisBits = BitConverter.DoubleToInt64Bits(testThis);
            return FastBitcount((ulong)testThisBits);
        }

        static private byte SparseBitcount(int testThis)
        {
            int count = 0;
            while (testThis != 0)
            {
                count++;
                testThis &= (testThis - 1);
            }

            return (byte)count;
        }
    }
}

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