test 'StringJoin" versus 'String.Join' in .NET 4.7

using System;
using System.Diagnostics;

static class Program
{
    static string[] rnds = new string[10000];

    static Program()
    {
        Stopwatch.GetTimestamp();
        Stopwatch.GetTimestamp();
        Stopwatch.GetTimestamp();
        Stopwatch.GetTimestamp();

        rnd = new Random((int)(Stopwatch.GetTimestamp() >> 5));

        for (int i = 0; i < rnds.Length; i++)
            rnds[i] = new string((Char)('!' + rnd.Next('~' - '!')), rnd.Next(7) + 1);

        // JIT warm-up
        var rgs = GetStrings();
        orderingA(rgs);
        orderingB(rgs);
        // reset timing
        t1 = t2 = 0;
    }

    readonly static Random rnd;
    static long t1, t2;

    static void Main(string[] args)
    {
        int i = 10000000;
        do
        {
            if ((i & 1) == 0)
                orderingA(GetStrings());
            else
                orderingB(GetStrings());
        }
        while (--i > 0);

        Console.WriteLine("'StringJoin' {0:#,###}", t1);
        Console.WriteLine("String.Join  {0:#,###}", t2);
        Console.WriteLine("{0:N2}", (t2 - t1) * 100.0 / Math.Min(t1, t2));
    }

    static string[] GetStrings()
    {
        var rgs = new String[rnd.Next(100) + 2];
        for (int i = 0; i < rgs.Length; i++)
            rgs[i] = rnds[rnd.Next(rnds.Length)];
        return rgs;
    }

    static void orderingA(String[] rgs)
    {
        test1(rgs);
        test2(rgs);
    }
    static void orderingB(String[] rgs)
    {
        test2(rgs);
        test1(rgs);
    }

    static void test1(String[] rgs)
    {
        var t = Stopwatch.GetTimestamp();
        alib.Enumerable.enum_ext.StringJoin(rgs);
        t1 += Stopwatch.GetTimestamp() - t;
    }
    static void test2(String[] rgs)
    {
        var t = Stopwatch.GetTimestamp();
        String.Join(String.Empty, rgs);
        t2 += Stopwatch.GetTimestamp() - t;
    }
};