Program.cs

using System;
using System.Diagnostics;
using System.Numerics;

namespace ConsoleApp1
{
    public class Program
    {
        public void Main(string[] args)
        {
            var vectorArray = new Vector<byte>[Vector<byte>.Count];

            for (int i = 0; i < Vector<byte>.Count; i++)
            {
                var byteArray = new byte[Vector<byte>.Count];

                byteArray[i] = 1;
                vectorArray[i] = new Vector<byte>(byteArray);
            }

            var stopWatch = new Stopwatch();
            stopWatch.Start();

            for (int i = 0; i < 10000000; i++)
            {
                for (int j = 0; j < Vector<byte>.Count; j++)
                {
                    FindFirstEqualByte2(vectorArray[j]);
                }
            }

            stopWatch.Stop();

            Console.WriteLine(stopWatch.ElapsedMilliseconds.ToString());
        }

        private static int FindFirstEqualByte(Vector<byte> chEquals)
        {
            // Quasi-tree search
            var vector64 = Vector.AsVectorInt64(chEquals);
            for (var i = 0; i < Vector<long>.Count; i++)
            {
                var longValue = vector64[i];
                if (longValue == 0) continue;

                var shift = i << 1;
                var offset = shift << 2;
                var vector32 = Vector.AsVectorInt32(chEquals);
                if (vector32[shift] != 0)
                {
                    if (chEquals[offset] != 0) return offset;
                    if (chEquals[++offset] != 0) return offset;
                    if (chEquals[++offset] != 0) return offset;
                    return ++offset;
                }
                offset += 4;
                if (chEquals[offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                return ++offset;
            }
            throw new InvalidOperationException();
        }

        private static int FindFirstEqualByte2(Vector<byte> chEquals)
        {
            var vector64 = Vector.AsVectorInt64(chEquals);
            for (var i = 0; i < Vector<long>.Count; i++)
            {
                var longValue = vector64[i];
                if (longValue == 0) continue;

                var offset = i << 3;
                if (chEquals[offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                if (chEquals[++offset] != 0) return offset;
                return ++offset;
            }
            throw new InvalidOperationException();
        }
    }
}