Suggest a possible optimization for static Color GetNamedColor(ReadOnlySpan<char> value).

[lsoft]

(a copy of dotnet/Microsoft.Maui.Graphics#495)

I write this into issue, because I'm not sure we want such optimizations at all.

The discussed method: https://github.com/dotnet/maui/blob/main/src/Graphics/src/Graphics/Color.cs#L757

Now, the method looks like

		static Color GetNamedColor(ReadOnlySpan<char> value)
		{
			// the longest built-in Color's name is much lower than this check, so we should not allocate here in a typical usage
			Span<char> loweredValue = value.Length <= 128 ? stackalloc char[value.Length] : new char[value.Length];

			int charsWritten = value.ToLowerInvariant(loweredValue);
			Debug.Assert(charsWritten == value.Length);

			// this should use the C# feature https://github.com/dotnet/csharplang/issues/1881, when it is available
			// for now, we need to allocate the lowered string
			return loweredValue.ToString() switch
			{
				"default" => default,
				"aliceblue" => Colors.AliceBlue,

                                 //big switch

				"yellow" => Colors.Yellow,
				"yellowgreen" => Colors.YellowGreen,
				_ => null
			};
		}

I found that there is the room for optimization. On my machine the data looks like (PTAL on allocations too):

BenchmarkDotNet=v0.13.2, OS=Windows 10 (10.0.19044.1586/21H2/November2021Update)
Intel Core i7-8550U CPU 1.80GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET SDK=7.0.100
  [Host]     : .NET 7.0.0 (7.0.22.51805), X64 RyuJIT AVX2
  DefaultJob : .NET 7.0.0 (7.0.22.51805), X64 RyuJIT AVX2

|                  Method |     Mean |     Error |    StdDev |   Gen0 | Allocated |
|------------------------ |---------:|----------:|----------:|-------:|----------:|
|      GetNamedColor_Orig | 6.106 us | 0.1194 us | 0.1058 us | 1.5106 |    6320 B |
| GetNamedColor_Generated | 4.302 us | 0.0661 us | 0.1158 us |      - |         - |

The benchmark method looks like:

        [Benchmark]
        public void GetNamedColor_Orig()
        {
            _ = GetNamedColor_Orig("default");
            _ = GetNamedColor_Orig("aliceblue");

           ... //all existing colors

            _ = GetNamedColor_Orig("yellow");
            _ = GetNamedColor_Orig("yellowgreen");
        }

The optimized method:

        static Color GetNamedColor(ReadOnlySpan<char> value)
        {
            // the longest built-in Color's name is much lower than this check, so we should not allocate here in a typical usage
            Span<char> loweredValue = value.Length <= 128 ? stackalloc char[value.Length] : new char[value.Length];

            int charsWritten = value.ToLowerInvariant(loweredValue);
            Debug.Assert(charsWritten == value.Length);

            return GetNamedColor(loweredValue);
        }

        private static Color GetNamedColor(Span<char> color)
        {
            string candidatecolor = default;
            Color resultcolor = default;
            switch (color.Length)
            {
                case 3:
                    switch (color[0])
                    {
                        case 'r': candidatecolor = "red"; resultcolor = Colors.Red; break;
                        case 't': candidatecolor = "tan"; resultcolor = Colors.Tan; break;
                    }
                    break;
                case 4:
                    switch (color.Slice(2, 2))
                    {
                        case "ua": candidatecolor = "aqua"; resultcolor = Colors.Aqua; break;
                        case "ue": candidatecolor = "blue"; resultcolor = Colors.Blue; break;
                        case "an": candidatecolor = "cyan"; resultcolor = Colors.Cyan; break;
                        case "ld": candidatecolor = "gold"; resultcolor = Colors.Gold; break;
                        case "ay": candidatecolor = "gray"; resultcolor = Colors.Gray; break;
                        case "ey": candidatecolor = "grey"; resultcolor = Colors.Grey; break;
                        case "me": candidatecolor = "lime"; resultcolor = Colors.Lime; break;
                        case "vy": candidatecolor = "navy"; resultcolor = Colors.Navy; break;
                        case "ru": candidatecolor = "peru"; resultcolor = Colors.Peru; break;
                        case "nk": candidatecolor = "pink"; resultcolor = Colors.Pink; break;
                        case "um": candidatecolor = "plum"; resultcolor = Colors.Plum; break;
                        case "ow": candidatecolor = "snow"; resultcolor = Colors.Snow; break;
                        case "al": candidatecolor = "teal"; resultcolor = Colors.Teal; break;
                    }
                    break;
                case 5:
                    switch (color.Slice(1, 2))
                    {
                        case "zu": candidatecolor = "azure"; resultcolor = Colors.Azure; break;
                        case "ei": candidatecolor = "beige"; resultcolor = Colors.Beige; break;
                        case "la": candidatecolor = "black"; resultcolor = Colors.Black; break;
                        case "ro": candidatecolor = "brown"; resultcolor = Colors.Brown; break;
                        case "or": candidatecolor = "coral"; resultcolor = Colors.Coral; break;
                        case "re": candidatecolor = "green"; resultcolor = Colors.Green; break;
                        case "vo": candidatecolor = "ivory"; resultcolor = Colors.Ivory; break;
                        case "ha": candidatecolor = "khaki"; resultcolor = Colors.Khaki; break;
                        case "in": candidatecolor = "linen"; resultcolor = Colors.Linen; break;
                        case "li": candidatecolor = "olive"; resultcolor = Colors.Olive; break;
                        case "he": candidatecolor = "wheat"; resultcolor = Colors.Wheat; break;
                        case "hi": candidatecolor = "white"; resultcolor = Colors.White; break;
                    }
                    break;
                case 6:
                    switch (color.Slice(1, 2))
                    {
                        case "is": candidatecolor = "bisque"; resultcolor = Colors.Bisque; break;
                        case "nd": candidatecolor = "indigo"; resultcolor = Colors.Indigo; break;
                        case "ar": candidatecolor = "maroon"; resultcolor = Colors.Maroon; break;
                        case "ra": candidatecolor = "orange"; resultcolor = Colors.Orange; break;
                        case "rc": candidatecolor = "orchid"; resultcolor = Colors.Orchid; break;
                        case "ur": candidatecolor = "purple"; resultcolor = Colors.Purple; break;
                        case "al": candidatecolor = "salmon"; resultcolor = Colors.Salmon; break;
                        case "ie": candidatecolor = "sienna"; resultcolor = Colors.Sienna; break;
                        case "il": candidatecolor = "silver"; resultcolor = Colors.Silver; break;
                        case "om": candidatecolor = "tomato"; resultcolor = Colors.Tomato; break;
                        case "io": candidatecolor = "violet"; resultcolor = Colors.Violet; break;
                        case "el": candidatecolor = "yellow"; resultcolor = Colors.Yellow; break;
                    }
                    break;
                case 7:
                    switch (color.Slice(5, 2))
                    {
                        case "lt": candidatecolor = "default"; resultcolor = default; break;
                        case "on": candidatecolor = "crimson"; resultcolor = Colors.Crimson; break;
                        case "ed": candidatecolor = "darkred"; resultcolor = Colors.DarkRed; break;
                        case "ay": candidatecolor = "dimgray"; resultcolor = Colors.DimGray; break;
                        case "ey": candidatecolor = "dimgrey"; resultcolor = Colors.DimGrey; break;
                        case "ia": candidatecolor = "fuchsia"; resultcolor = Colors.Fuchsia; break;
                        case "nk": candidatecolor = "hotpink"; resultcolor = Colors.HotPink; break;
                        case "ta": candidatecolor = "magenta"; resultcolor = Colors.Magenta; break;
                        case "ce": candidatecolor = "oldlace"; resultcolor = Colors.OldLace; break;
                        case "ue": candidatecolor = "skyblue"; resultcolor = Colors.SkyBlue; break;
                        case "le": candidatecolor = "thistle"; resultcolor = Colors.Thistle; break;
                    }
                    break;
                case 8:
                    switch (color.Slice(6, 2))
                    {
                        case "lk": candidatecolor = "cornsilk"; resultcolor = Colors.Cornsilk; break;
                        case "ue": candidatecolor = "darkblue"; resultcolor = Colors.DarkBlue; break;
                        case "an": candidatecolor = "darkcyan"; resultcolor = Colors.DarkCyan; break;
                        case "ay": candidatecolor = "darkgray"; resultcolor = Colors.DarkGray; break;
                        case "ey": candidatecolor = "darkgrey"; resultcolor = Colors.DarkGrey; break;
                        case "nk": candidatecolor = "deeppink"; resultcolor = Colors.DeepPink; break;
                        case "ew": candidatecolor = "honeydew"; resultcolor = Colors.Honeydew; break;
                        case "er": candidatecolor = "lavender"; resultcolor = Colors.Lavender; break;
                        case "in": candidatecolor = "moccasin"; resultcolor = Colors.Moccasin; break;
                        case "en": candidatecolor = "seagreen"; resultcolor = Colors.SeaGreen; break;
                        case "ll": candidatecolor = "seashell"; resultcolor = Colors.SeaShell; break;
                    }
                    break;
                case 9:
                    switch ((color[0] << 0) + (color[1] << 1) + (color[6] << 2) + (color[7] << 3))
                    {
                        case ('a' << 0) + ('l' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "aliceblue"; resultcolor = Colors.AliceBlue; break;
                        case ('b' << 0) + ('u' << 1) + ('o' << 2) + ('o' << 3): candidatecolor = "burlywood"; resultcolor = Colors.BurlyWood; break;
                        case ('c' << 0) + ('a' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "cadetblue"; resultcolor = Colors.CadetBlue; break;
                        case ('c' << 0) + ('h' << 1) + ('a' << 2) + ('t' << 3): candidatecolor = "chocolate"; resultcolor = Colors.Chocolate; break;
                        case ('d' << 0) + ('a' << 1) + ('e' << 2) + ('e' << 3): candidatecolor = "darkgreen"; resultcolor = Colors.DarkGreen; break;
                        case ('d' << 0) + ('a' << 1) + ('a' << 2) + ('k' << 3): candidatecolor = "darkkhaki"; resultcolor = Colors.DarkKhaki; break;
                        case ('f' << 0) + ('i' << 1) + ('i' << 2) + ('c' << 3): candidatecolor = "firebrick"; resultcolor = Colors.Firebrick; break;
                        case ('g' << 0) + ('a' << 1) + ('o' << 2) + ('r' << 3): candidatecolor = "gainsboro"; resultcolor = Colors.Gainsboro; break;
                        case ('g' << 0) + ('o' << 1) + ('r' << 2) + ('o' << 3): candidatecolor = "goldenrod"; resultcolor = Colors.Goldenrod; break;
                        case ('i' << 0) + ('n' << 1) + ('r' << 2) + ('e' << 3): candidatecolor = "indianred"; resultcolor = Colors.IndianRed; break;
                        case ('l' << 0) + ('a' << 1) + ('e' << 2) + ('e' << 3): candidatecolor = "lawngreen"; resultcolor = Colors.LawnGreen; break;
                        case ('l' << 0) + ('i' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "lightblue"; resultcolor = Colors.LightBlue; break;
                        case ('l' << 0) + ('i' << 1) + ('y' << 2) + ('a' << 3): candidatecolor = "lightcyan"; resultcolor = Colors.LightCyan; break;
                        case ('l' << 0) + ('i' << 1) + ('r' << 2) + ('e' << 3): candidatecolor = "lightgrey"; resultcolor = Colors.LightGrey; break;
                        case ('l' << 0) + ('i' << 1) + ('r' << 2) + ('a' << 3): candidatecolor = "lightgray"; resultcolor = Colors.LightGray; break;
                        case ('l' << 0) + ('i' << 1) + ('i' << 2) + ('n' << 3): candidatecolor = "lightpink"; resultcolor = Colors.LightPink; break;
                        case ('l' << 0) + ('i' << 1) + ('e' << 2) + ('e' << 3): candidatecolor = "limegreen"; resultcolor = Colors.LimeGreen; break;
                        case ('m' << 0) + ('i' << 1) + ('e' << 2) + ('a' << 3): candidatecolor = "mintcream"; resultcolor = Colors.MintCream; break;
                        case ('m' << 0) + ('i' << 1) + ('o' << 2) + ('s' << 3): candidatecolor = "mistyrose"; resultcolor = Colors.MistyRose; break;
                        case ('o' << 0) + ('l' << 1) + ('r' << 2) + ('a' << 3): candidatecolor = "olivedrab"; resultcolor = Colors.OliveDrab; break;
                        case ('o' << 0) + ('r' << 1) + ('r' << 2) + ('e' << 3): candidatecolor = "orangered"; resultcolor = Colors.OrangeRed; break;
                        case ('p' << 0) + ('a' << 1) + ('e' << 2) + ('e' << 3): candidatecolor = "palegreen"; resultcolor = Colors.PaleGreen; break;
                        case ('p' << 0) + ('e' << 1) + ('u' << 2) + ('f' << 3): candidatecolor = "peachpuff"; resultcolor = Colors.PeachPuff; break;
                        case ('r' << 0) + ('o' << 1) + ('o' << 2) + ('w' << 3): candidatecolor = "rosybrown"; resultcolor = Colors.RosyBrown; break;
                        case ('r' << 0) + ('o' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "royalblue"; resultcolor = Colors.RoyalBlue; break;
                        case ('s' << 0) + ('l' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "slateblue"; resultcolor = Colors.SlateBlue; break;
                        case ('s' << 0) + ('l' << 1) + ('r' << 2) + ('a' << 3): candidatecolor = "slategray"; resultcolor = Colors.SlateGray; break;
                        case ('s' << 0) + ('l' << 1) + ('r' << 2) + ('e' << 3): candidatecolor = "slategrey"; resultcolor = Colors.SlateGrey; break;
                        case ('s' << 0) + ('t' << 1) + ('l' << 2) + ('u' << 3): candidatecolor = "steelblue"; resultcolor = Colors.SteelBlue; break;
                        case ('t' << 0) + ('u' << 1) + ('i' << 2) + ('s' << 3): candidatecolor = "turquoise"; resultcolor = Colors.Turquoise; break;
                    }
                    break;
                case 10:
                    switch (color.Slice(3, 4))
                    {
                        case "amar": candidatecolor = "aquamarine"; resultcolor = Colors.Aquamarine; break;
                        case "evio": candidatecolor = "blueviolet"; resultcolor = Colors.BlueViolet; break;
                        case "rtre": candidatecolor = "chartreuse"; resultcolor = Colors.Chartreuse; break;
                        case "kora": candidatecolor = "darkorange"; resultcolor = Colors.DarkOrange; break;
                        case "korc": candidatecolor = "darkorchid"; resultcolor = Colors.DarkOrchid; break;
                        case "ksal": candidatecolor = "darksalmon"; resultcolor = Colors.DarkSalmon; break;
                        case "kvio": candidatecolor = "darkviolet"; resultcolor = Colors.DarkViolet; break;
                        case "gerb": candidatecolor = "dodgerblue"; resultcolor = Colors.DodgerBlue; break;
                        case "stwh": candidatecolor = "ghostwhite"; resultcolor = Colors.GhostWhite; break;
                        case "htco": candidatecolor = "lightcoral"; resultcolor = Colors.LightCoral; break;
                        case "htgr": candidatecolor = "lightgreen"; resultcolor = Colors.LightGreen; break;
                        case "iumb": candidatecolor = "mediumblue"; resultcolor = Colors.MediumBlue; break;
                        case "ayaw": candidatecolor = "papayawhip"; resultcolor = Colors.PapayaWhip; break;
                        case "derb": candidatecolor = "powderblue"; resultcolor = Colors.PowderBlue; break;
                        case "dybr": candidatecolor = "sandybrown"; resultcolor = Colors.SandyBrown; break;
                        case "tesm": candidatecolor = "whitesmoke"; resultcolor = Colors.WhiteSmoke; break;
                    }
                    break;
                case 11:
                    switch (color.Slice(4, 2))
                    {
                        case "ma": candidatecolor = "darkmagenta"; resultcolor = Colors.DarkMagenta; break;
                        case "sk": candidatecolor = "deepskyblue"; resultcolor = Colors.DeepSkyBlue; break;
                        case "al": candidatecolor = "floralwhite"; resultcolor = Colors.FloralWhite; break;
                        case "st": candidatecolor = "forestgreen"; resultcolor = Colors.ForestGreen; break;
                        case "ny": candidatecolor = "greenyellow"; resultcolor = Colors.GreenYellow; break;
                        case "ts": candidatecolor = "lightsalmon"; resultcolor = Colors.LightSalmon; break;
                        case "ty": candidatecolor = "lightyellow"; resultcolor = Colors.LightYellow; break;
                        case "jo": candidatecolor = "navajowhite"; resultcolor = Colors.NavajoWhite; break;
                        case "le": candidatecolor = "saddlebrown"; resultcolor = Colors.SaddleBrown; break;
                        case "ng": candidatecolor = "springgreen"; resultcolor = Colors.SpringGreen; break;
                        case "sp": candidatecolor = "transparent"; resultcolor = Colors.Transparent; break;
                        case "ow": candidatecolor = "yellowgreen"; resultcolor = Colors.YellowGreen; break;
                    }
                    break;
                case 12:
                    switch (color[7])
                    {
                        case 'w': candidatecolor = "antiquewhite"; resultcolor = Colors.AntiqueWhite; break;
                        case 'g': candidatecolor = "darkseagreen"; resultcolor = Colors.DarkSeaGreen; break;
                        case 'i': candidatecolor = "lemonchiffon"; resultcolor = Colors.LemonChiffon; break;
                        case 'y': candidatecolor = "lightskyblue"; resultcolor = Colors.LightSkyBlue; break;
                        case 'r': candidatecolor = "mediumorchid"; resultcolor = Colors.MediumOrchid; break;
                        case 'u': candidatecolor = "mediumpurple"; resultcolor = Colors.MediumPurple; break;
                        case 't': candidatecolor = "midnightblue"; resultcolor = Colors.MidnightBlue; break;
                    }
                    break;
                case 13:
                    switch ((color[0] << 0) + (color[4] << 1) + (color[11] << 2))
                    {
                        case ('d' << 0) + ('g' << 1) + ('o' << 2): candidatecolor = "darkgoldenrod"; resultcolor = Colors.DarkGoldenrod; break;
                        case ('d' << 0) + ('s' << 1) + ('u' << 2): candidatecolor = "darkslateblue"; resultcolor = Colors.DarkSlateBlue; break;
                        case ('d' << 0) + ('s' << 1) + ('a' << 2): candidatecolor = "darkslategray"; resultcolor = Colors.DarkSlateGray; break;
                        case ('d' << 0) + ('s' << 1) + ('e' << 2): candidatecolor = "darkslategrey"; resultcolor = Colors.DarkSlateGrey; break;
                        case ('d' << 0) + ('t' << 1) + ('s' << 2): candidatecolor = "darkturquoise"; resultcolor = Colors.DarkTurquoise; break;
                        case ('l' << 0) + ('n' << 1) + ('s' << 2): candidatecolor = "lavenderblush"; resultcolor = Colors.LavenderBlush; break;
                        case ('l' << 0) + ('t' << 1) + ('e' << 2): candidatecolor = "lightseagreen"; resultcolor = Colors.LightSeaGreen; break;
                        case ('p' << 0) + ('g' << 1) + ('o' << 2): candidatecolor = "palegoldenrod"; resultcolor = Colors.PaleGoldenrod; break;
                        case ('p' << 0) + ('t' << 1) + ('s' << 2): candidatecolor = "paleturquoise"; resultcolor = Colors.PaleTurquoise; break;
                        case ('p' << 0) + ('v' << 1) + ('e' << 2): candidatecolor = "palevioletred"; resultcolor = Colors.PaleVioletRed; break;
                    }
                    break;
                case 14:
                    switch ((color[2] << 0) + (color[12] << 1))
                    {
                        case ('a' << 0) + ('n' << 1): candidatecolor = "blanchedalmond"; resultcolor = Colors.BlanchedAlmond; break;
                        case ('r' << 0) + ('u' << 1): candidatecolor = "cornflowerblue"; resultcolor = Colors.CornflowerBlue; break;
                        case ('r' << 0) + ('e' << 1): candidatecolor = "darkolivegreen"; resultcolor = Colors.DarkOliveGreen; break;
                        case ('g' << 0) + ('a' << 1): candidatecolor = "lightslategray"; resultcolor = Colors.LightSlateGray; break;
                        case ('g' << 0) + ('e' << 1): candidatecolor = "lightslategrey"; resultcolor = Colors.LightSlateGrey; break;
                        case ('g' << 0) + ('u' << 1): candidatecolor = "lightsteelblue"; resultcolor = Colors.LightSteelBlue; break;
                        case ('d' << 0) + ('e' << 1): candidatecolor = "mediumseagreen"; resultcolor = Colors.MediumSeaGreen; break;
                    }
                    break;
                case 15:
                    switch (color[6])
                    {
                        case 's': candidatecolor = "mediumslateblue"; resultcolor = Colors.MediumSlateBlue; break;
                        case 't': candidatecolor = "mediumturquoise"; resultcolor = Colors.MediumTurquoise; break;
                        case 'v': candidatecolor = "mediumvioletred"; resultcolor = Colors.MediumVioletRed; break;
                    }
                    break;
                case 16: candidatecolor = "mediumaquamarine"; resultcolor = Colors.MediumAquamarine; break;
                case 17: candidatecolor = "mediumspringgreen"; resultcolor = Colors.MediumSpringGreen; break;
                case 20: candidatecolor = "lightgoldenrodyellow"; resultcolor = Colors.LightGoldenrodYellow; break;
            }

            if(MemoryExtensions.SequenceEqual(candidatecolor.AsSpan(), color))
            //if(MemoryExtensions.Equals(candidatecolor.AsSpan(), color, StringComparison.Ordinal))
            {
                return resultcolor;
            }

            return null;
        }

(the idea taken from from dotnet/roslyn#56374)

Few issues to mention:

1. optimized version is bigger. it may be undesirable.
2. optimized version is harder to understand and modify (for example for adding a new color).
3. I do not check this code on a device because lack of possibility! I cheched only on PC.

If maintainers decides that this approach is fine, few additional points:

1. I have an Incremental Source Generator that able to generate this body easily. Such generator can be included in this project and disable 2nd issue above.
2. Also, other places with switch-over-strings can benefit from that source generator. I would like to play with them. Is there any?

Any thoughts? Thanks.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.