mandelbrot C# .NET Core #9 program

/* The Computer Language Benchmarks Game
   https://salsa.debian.org/benchmarksgame-team/benchmarksgame/

   started with Java #2 program (Krause/Whipkey/Bennet/AhnTran/Enotus/Stalcup)
   adapted for C# by Jan de Vaan
   simplified and optimised to use TPL by Anthony Lloyd
   optimized to use Vector<double> by Tanner Gooding
   small optimisations by Anthony Lloyd
   modified by Grigory Perepechko
*/

using System;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;

public class MandelBrot
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static unsafe byte GetByte(double* pCrb, double Ciby)
    {
        var res = 0;
        for (var i=0; i<8; i+=2)
        {
            var vCrbx = Unsafe.Read<Vector<double>>(pCrb+i);
            var vCiby = new Vector<double>(Ciby);
            var Zr = vCrbx;
            var Zi = vCiby;
            int b = 0, j = 49;
            do
            {
                for (int counter = 0; counter < 7; counter++)
                {
                    var nZr = Zr * Zr - Zi * Zi + vCrbx;
                    var ZrZi = Zr * Zi;
                    Zi = ZrZi + ZrZi + vCiby;
                    Zr = nZr;
                    j--;
                }

                var t = Zr * Zr + Zi * Zi;
                if (t[0]>4.0) { b|=2; if (b==3) break; }
                if (t[1]>4.0) { b|=1; if (b==3) break; }
            } while (j>0);
            res = (res << 2) + b;
        }
        return (byte)(res^-1);
    }
    public static unsafe void Main(string[] args)
    {
        var size = args.Length==0 ? 200 : int.Parse(args[0]);
        Console.Out.WriteAsync(String.Concat("P4\n",size," ",size,"\n"));
        var Crb = new double[size+2];
        var lineLength = size >> 3;
        var data = new byte[size * lineLength];
        fixed (double* pCrb = &Crb[0])
        fixed (byte* pdata = &data[0])
        {
            var value = new Vector<double>(
                  new double[] {0,1,0,0,0,0,0,0}
            );
            var invN = new Vector<double>(2.0/size);
            var onePtFive = new Vector<double>(1.5);
            var step = new Vector<double>(2);
            for (var i=0; i<size; i+=2)
            {
                Unsafe.Write(pCrb+i, value*invN-onePtFive);
                value += step;
            }
            var _Crb = pCrb;
            var _pdata = pdata;
            Parallel.For(0, size, y =>
            {
                var Ciby = _Crb[y]+0.5;
                for (var x=0; x<lineLength; x++)
                {
                    _pdata[y*lineLength+x] = GetByte(_Crb+x*8, Ciby);
                }
            });
            Console.OpenStandardOutput().Write(data, 0, data.Length);
        }
    }
}
    

NOTES:
64-bit Ubuntu quad core
.NET Core SDK   3.1.201
Host Version: 3.1.3; Commit: 4a9f85e9f8
<ServerGarbageCollection>true
<ConcurrentGarbageCollection>true


Thu, 07 May 2020 20:55:31 GMT

MAKE:
cp mandelbrot.csharpcore-9.csharpcore Program.cs
cp Include/csharpcore/tmp.csproj .
mkdir obj
cp Include/csharpcore/project.assets.json ./obj
/usr/bin/dotnet build -c Release --no-restore
Microsoft (R) Build Engine version 16.5.0+d4cbfca49 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  tmp -> /home/dunham/benchmarksgame_quadcore/mandelbrot/tmp/bin/Release/netcoreapp3.1/tmp.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:05.06

7.88s to complete and log all make actions

COMMAND LINE:
/usr/bin/dotnet ./bin/Release/netcoreapp3.1/tmp.dll 16000

(BINARY) PROGRAM OUTPUT NOT SHOWN