.NET Core 3.1, IndexOf(char) test case

gistfile1.txt

	static class Program
	{
		/// <summary>
		///  The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main()
		{
			DoTest();
		}

		static void DoTest()
		{
			var fileName = @"d:\text.txt";
			Text text = default;

			var enc = CharsetDetector.DetectFromFile(fileName).Detected;
			foreach (ReadOnlySpan<char> line in File.ReadLines(fileName, Encoding.GetEncoding(enc.EncodingName)))
			{
				text.Add(line);
			}

			var sw = new Stopwatch();
			sw.Start();
			var cnt = 0;
			for (var i = 0; i < text.LineCount; i++)
			{
				var l = text[i];
				var p = (UnsafePointer<char>)text[i];
				cnt += CountOf1(p, l.Length, '\t');
			}

			sw.Stop();
			var c1 = cnt;
			var t1 = sw.ElapsedMilliseconds;

			sw = new Stopwatch();
			sw.Start();
			cnt = 0;
			for (var i = 0; i < text.LineCount; i++)
			{
				var l = text[i];
				var p = (UnsafePointer<char>) text[i];
				cnt += CountOf2(p, l.Length, '\t');
			}

			sw.Stop();
			var c2 = cnt;
			var t2 = sw.ElapsedMilliseconds;

			sw = new Stopwatch();
			sw.Start();
			cnt = 0;
			for (var i = 0; i < text.LineCount; i++)
			{
				var l = text[i];
				var p = (UnsafePointer<char>)text[i];
				cnt += CountOf3(p, l.Length, '\t');
			}

			sw.Stop();
			var c3 = cnt;
			var t3 = sw.ElapsedMilliseconds;

			File.WriteAllLines(@"d:\indexof.txt", new[] {$"Brute: cnt={c1}, ms={t1}", $"Span: cnt={c2}, ms={t2}", $"Intrinsics: cnt={c3}, ms={t3}",});
		}


		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static int IndexOf1(UnsafePointer<char> chars, int length, char element, int offset = 0)
		{
			for (var i = offset; i < length; i++)
			{
				if (chars[i] != element) continue;
				return i;
			}

			return -1;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static int CountOf1(UnsafePointer<char> chars, int length, char c, int offset = 0)
		{
			var cnt = 0;
			while (true)
			{
				var i = IndexOf1(chars, length, c, offset);
				if (i < 0) break;
				cnt++;
				offset += ++i;
			}

			return cnt;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static unsafe int IndexOf2(UnsafePointer<char> chars, int length, char element, int offset = 0)
		{
			if (offset >= length) return -1;
			return new Span<char>((void*)(chars + offset), length - offset).IndexOf(element);
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static int CountOf2(UnsafePointer<char> chars, int length, char c, int offset = 0)
		{
			var cnt = 0;
			while (true)
			{
				var i = IndexOf2(chars, length, c, offset);
				if (i < 0) break;
				cnt++;
				offset += ++i;
			}

			return cnt;
		}


		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static unsafe int IndexOf3(UnsafePointer<char> chars, int length, char element, int offset)
		{
			if (offset >= length) return -1;
			return Intrinsics.IndexOf((char*)(chars + offset), (length - offset), element);
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
		public static int CountOf3(UnsafePointer<char> chars, int length, char c, int offset = 0)
		{
			var cnt = 0;
			while (true)
			{
				var i = IndexOf3(chars, length, c, offset);
				if (i < 0) break;
				cnt++;
				offset += ++i;
			}

			return cnt;
		}
	}