How can I convert BitArray to single int?

Question

How can I convert BitArray to a single int?

Solution 1

private int getIntFromBitArray(BitArray bitArray)
{

    if (bitArray.Length > 32)
        throw new ArgumentException("Argument length shall be at most 32 bits.");

    int[] array = new int[1];
    bitArray.CopyTo(array, 0);
    return array[0];

}

Solution 2

private int getIntFromBitArray(BitArray bitArray)
{
    int value = 0;

    for (int i = 0; i < bitArray.Count; i++)
    {
        if (bitArray[i])
            value += Convert.ToInt16(Math.Pow(2, i));
    }

    return value;
}

Solution 3

This version:

• works for up to 64 bits
• doesn't rely on knowledge of BitArray implementation details
• doesn't needlessly allocate memory
• doesn't throw any exceptions (feel free to add a check if you expect more bits)
• should be more than reasonably performant

Implementation:

public static ulong BitArrayToU64(BitArray ba)
{
    var len = Math.Min(64, ba.Count);
    ulong n = 0;
    for (int i = 0; i < len; i++) {
        if (ba.Get(i))
            n |= 1UL << i;
    }
    return n;
}

Comments

[Brandon Boone]

BitArray to int Array or literally a BitArray to a single integer?

[codekaizen]

Wow... I didn't think this would work to put all the bits into one integer value - but it does!

[coder_bro]

Refer this: codereview.stackexchange.com/questions/3796/… Need to check the length of bitArray

[Austin Henley]

Can you explain why the OP should use this over the other solution?

[K4KNOWLEDGE]

@AustinHenley I wrote this solution for debug purposes. I can step through my code to see how the number is being converted. I'm not sure if you can do that with the first solution.

[tec-goblin]

It's also interesting to know that the first solution is not available on WinRT (probably because of the way ARM processors save the numbers)

[Mike Christiansen]

I have to use this because its not available on ARM.

[ChristopheD]

The .NET Core stack may not have BitArray.CopyTo. That being said, why not 1 << i rather than Convert.ToInt16(Math.Pow(2, i))?

[harold]

OK but you should make it |= and (short)(1 << bitToSet) to make it more obvious at a glance. It's not like this code is incomprehensible, but it relies on the combination of some "carefully chosen coincidences" instead of just obviously doing the right thing.

[nvoigt]

Can you explain how this is better than the accepted solution from 7 years ago? Is it faster, more accurate, better at error handling, using less memory?

[Jozef Benikovský]

Nice trick, however it could have issues related to byte order (endianess) on various platforms. It would be better to use byte array as destination for bit array copy and use BitConverter.ToInt32(array, 0) method afterwards.