C# power set for large set sizes

Recently for a Microsoft ML.NET machine learning project I wanted to generate a power set for choosing the optimal set of features for the model. Unfortunately all the existing examples I found were limited to a set size of 31 or 32 as they were using integer types and also attempting to return the complete power set in a single collection bounding them to collection size limits.

My machine learning model contained 33 features and while a power set of that size would contain over eight billion sets I just wanted to evaluate power sets with 31-33 elements as an initial step which yields a more reasonable set size of 529. To solve the problem I wrote the following code that uses 64-bit unsigned integers and returns the sets as an enumerable to avoid the excessive memory use of attempting to create the complete collection in memory.

C# Source Code

static void Main()
{
	// Following test of power set of length 31 to 33 takes around 
	// six minutes on a Core i7-4770K CPU @ 3.5 GHz.

	var testData = Enumerable.Range(0, 33).ToArray();
	int totalCount = 0;
	foreach (var set in PowerSet(testData, 31))
	{
		Console.WriteLine(string.Join(",", set));
		totalCount++;
	}
	Console.WriteLine(totalCount);
}

public static IEnumerable PowerSet(T[] seq, int minLength = 0)
{
	if (seq == null)
	{
		throw new ArgumentNullException(nameof(seq));
	}
	var enumerable = Enumerable.Range(0, seq.Length);
	ulong powerSetSize = 1UL << seq.Length;
	ulong startPoint = (1UL << minLength) - 1;
	for (ulong curVal = startPoint; curVal < powerSetSize; curVal++)
	{
		int bitCount = CountBits(curVal);
		if (bitCount >= minLength)
		{
			yield return enumerable
				.Where(e => (curVal & (1UL << e)) > 0)
				.Select(e => seq[e])
				.ToArray();
		}
	}
}

// Following by Jon Skeet / Brian Kernighan, see https://stackoverflow.com/a/12171691/1599751
public static int CountBits(ulong value)
{
	int count = 0;
	while (value != 0)
	{
		count++;
		value &= value - 1;
	}
	return count;
}