Introduce methods

Rationale and Usage

Checking if a number is a power of 2 is a relatively common operation. There's always the

(value & (value - 1)) == 0 && value != 0

bit twiddle hack, but it is verbose, clunky, not immediately clear, not ideal performance wise, and requires remembering.
Introducing a simple API that is equivalent would be useful.

Proposed API

namespace System.Numerics
{
    public static class BitOperations
    {
        public static bool IsPow2(int value);
        public static bool IsPow2(uint value);
        public static bool IsPow2(long value);
        public static bool IsPow2(ulong value);
    }
}

Details

It uses a popcount operation where possible, else uses the bit twiddle hack.

Open Questions

• Should we consider 0 a power of 2?

  • The classic bit twiddle doesn't

• Should we have methods for float/double (or even decimal)?

  • With float/double you can compare the mantissa to 0.5 I believe, but it isn't really
    "in character" with the rest of BitOperations (which generally only supports integral types)

Pull Request

#36163