group.cs

using System;
using System.Collections;
using System.Runtime.Intrinsics.X86;
using System.Runtime.Intrinsics;

public struct BitMask
{
    private ushort mask;
    BitMask(ushort mask_) => mask = mask_;

    // Summary:
    //   Compares 16 bytes to see if they match a predicate, in parallel
    unsafe BitMask matches(byte[] vec, byte predicate)
    {
        fixed (byte* v = &vec[0]) {
            var vector = Sse42.LoadVector128(v);
            var pred = Vector128.Create(predicate);
            return new BitMask(
                (ushort)Sse42.MoveMask(
                    Sse42.CompareEqual(vector, pred)
                )
            );
        }
    }
}
public struct Group
{
    private Vector128<byte> vector;
    private const ulong WIDTH = 16; // for SOME REASON we cannot do `unsafe { sizeof(Vector128<byte>) }`
    public const byte EMPTY = 128;     // 0b10000000
    public const byte DELETED = 254;   // 0b11111111
    public const byte SENTINEL = 255;  // 0b11111110


    // Summary:
    //  value:
    //    the value to which _all_ members of the group will be initialized to
    Group(byte value) => vector = Vector128.Create(value);

    // Parameters:
    //   slice:
    //     MUST be a length 16 byte array
    // 
    // Exceptions:
    //   ArgumentException: Thrown if you do not pass a length 16 byte array
    unsafe Group(byte[] slice)
    {
        if (slice.Length != 16) {
            throw new ArgumentException("Input MUST be length 16 >:(");
        }
        fixed (byte* v = &slice[0]) {
            vector = Sse42.LoadVector128(v);
        }
    }

    // Summary:
    //  Gets a bitmask of all the values in the vector 
    ushort BitMask()
    {
        return (ushort)Sse2.MoveMask(vector);
    }

    // Summary:
    //   Here, Empty signifies that there are no matching
    //   elements contained in the group
    bool IsEmpty()
    {
        return this.BitMask() == 0;
    }
}