CopySign_Double.cs

[CoreJob]
public class CopySignDBenchmark
{
    public enum SignType
    {
        Random,
        Same,
        Different,
        Alternating
    }

    private const int Seed = 98412310;

    private const int Count = 32_768;

    private double[] _dest;

    public double[] Source1 { get; private set; }

    public double[] Source2 { get; private set; }

    [Params(SignType.Same, SignType.Different, SignType.Alternating, SignType.Random)]
    public SignType Scenario { get; set; }

    [GlobalSetup]
    public void Setup()
    {
        Source1 = new double[Count];
        Source2 = new double[Count];
        _dest = new double[Count];

        var rng = new Random(Seed);

        for (int i = 0; i < Count; i++)
        {
            Source1[i] = rng.NextDouble();
            Source2[i] = rng.NextDouble();

            if (Scenario == SignType.Different)
            {
                Source2[i] = -Source2[i];
            }
            else if (Scenario == SignType.Alternating)
            {
                // Every other element should be inverted

                if ((i % 2) == 0)
                {
                    Source2[i] = -Source2[i];
                }
            }
            else if (Scenario == SignType.Random)
            {
                var bits = BitConverter.DoubleToInt64Bits(Source2[i]);

                // Value generated is already random, so do a parity check
                // to determine if we should invert the value or not

                if ((BitOperations.PopCount((ulong)bits) % 2) == 0)
                {
                    Source2[i] = -Source2[i];
                }
            }
        }
    }

    [Benchmark]
    //[Arguments(1f, 1f)]
    //[Arguments(1f, -1f)]
    //[Arguments(-1f, -1f)]
    public void Standard()
    {
        for (var i = 0; i < Count; i++)
        {
            double x = Source1[i];
            double y = Source2[i];

            // This method is required to work for all inputs,
            // including NaN, so we operate on the raw bits.

            long xbits = BitConverter.DoubleToInt64Bits(x);
            long ybits = BitConverter.DoubleToInt64Bits(y);

            // If the sign bits of x and y are not the same,
            // flip the sign bit of x and return the new value;
            // otherwise, just return x

            if ((xbits ^ ybits) < 0)
            {
                x = BitConverter.Int64BitsToDouble(xbits ^ long.MinValue);
            }

            _dest[i] = x;
        }
    }

    [Benchmark]
    //[Arguments(1f, 1f)]
    //[Arguments(1f, -1f)]
    //[Arguments(-1f, -1f)]
    public void John()
    {
        for (var i = 0; i < Count; i++)
        {
            double x = Source1[i];
            double y = Source2[i];

            // This method is required to work for all inputs,
            // including NaN, so we operate on the raw bits.

            long xbits = BitConverter.DoubleToInt64Bits(x);
            long ybits = BitConverter.DoubleToInt64Bits(y);

            // Remove the sign from x, and remove everything but the sign from y

            const long signMask
                = unchecked((long)0b_1000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000);

            xbits &= ~signMask;
            ybits &= signMask;

            // Simply OR them to get the correct sign
            x = BitConverter.Int64BitsToDouble(xbits | ybits);

            _dest[i] = x;
        }
    }

    [Benchmark]
    //[Arguments(1f, 1f)]
    //[Arguments(1f, -1f)]
    //[Arguments(-1f, -1f)]
    public void John_Intrinsic()
    {
        for (var i = 0; i < Count; i++)
        {
            double x = Source1[i];
            double y = Source2[i];

            const long signMask
                = unchecked((long)0b_1000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000__0000_0000);

            if (Sse.IsSupported)
            {
                var xvec = Vector128.CreateScalarUnsafe(x).AsSingle();
                var yvec = Vector128.CreateScalarUnsafe(y).AsSingle();

                xvec = Sse.And(xvec, Vector128.CreateScalarUnsafe(~signMask).AsSingle());
                yvec = Sse.And(yvec, Vector128.CreateScalarUnsafe(signMask).AsSingle());

                x = Sse.Or(xvec, yvec).AsDouble().ToScalar();
            }
            else
            {
                // This method is required to work for all inputs,
                // including NaN, so we operate on the raw bits.

                long xbits = BitConverter.DoubleToInt64Bits(x);
                long ybits = BitConverter.DoubleToInt64Bits(y);

                // Remove the sign from x, and remove everything but the sign from y

                xbits &= ~signMask;
                ybits &= signMask;

                // Simply OR them to get the correct sign
                x = BitConverter.Int64BitsToDouble(xbits | ybits);
            }
            _dest[i] = x;
        }
    }
}