using System;

public class Program

{

    public static void Main(string[] args)

    {

        const ulong mask = 2196870UL;   // 001000011000010110000110 (Eight ones)

        const ulong input = 15378090UL; // 111010101010011010101010

        //                      SAME BITS: --x-----x----x--x-----x- (Five same)

        Console.WriteLine(dendrite(input, mask)); // Should print 5/8 = 0.625

    }

    static float dendrite(ulong input, ulong mask)

    {

        // get bits that are same (0 or 1) in input and mask

        ulong samebits = mask & ~(input ^ mask);

        // count number of same bits

        int correct = cardinality(samebits);

        // count number of bits in mask

        int inmask = cardinality(mask);

        // compute fraction (0.0 to 1.0)

        return inmask == 0 ? 0f : correct / (float)inmask;

    }

    // this is a little hack to count the number of bits set to one in a 64-bit word

    static int cardinality(ulong word)

    {

        const ulong mult = 0x0101010101010101;

        const ulong mask1h = (~0UL) / 3 << 1;

        const ulong mask2l = (~0UL) / 5;

        const ulong mask4l = (~0UL) / 17;

        word -= (mask1h & word) >> 1;

        word = (word & mask2l) + ((word >> 2) & mask2l);

        word += word >> 4;

        word &= mask4l;

        return (int)((word * mult) >> 56);

    }

}