Move property out of loop

Sqids.sln

@@ -11,6 +11,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "test", "test", "{5B69EBB5-A
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Sqids.Tests", "test\Sqids.Tests\Sqids.Tests.csproj", "{26D42DEF-5A42-436C-8B80-44AA4917BFC1}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "benchmark", "benchmark", "{F165CB60-0269-4F53-8F6C-F61EF172947C}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Sqids.Benchmarks", "benchmark\Sqids.Benchmarks\Sqids.Benchmarks.csproj", "{7892A604-1098-4088-A806-01787BE78521}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -28,9 +32,14 @@ Global
 		{26D42DEF-5A42-436C-8B80-44AA4917BFC1}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{26D42DEF-5A42-436C-8B80-44AA4917BFC1}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{26D42DEF-5A42-436C-8B80-44AA4917BFC1}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7892A604-1098-4088-A806-01787BE78521}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7892A604-1098-4088-A806-01787BE78521}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7892A604-1098-4088-A806-01787BE78521}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7892A604-1098-4088-A806-01787BE78521}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{387B307E-04C6-4B8E-BE50-03FF91307070} = {FC64F776-DE51-4BFF-91D5-0ECFEEF5CCAC}
 		{26D42DEF-5A42-436C-8B80-44AA4917BFC1} = {5B69EBB5-A05C-4DCB-9355-D010B0A093AE}
+		{7892A604-1098-4088-A806-01787BE78521} = {F165CB60-0269-4F53-8F6C-F61EF172947C}
 	EndGlobalSection
 EndGlobal

benchmark/Sqids.Benchmarks/EncodeBenchmark.cs

@@ -0,0 +1,31 @@
+using BenchmarkDotNet.Attributes;
+
+namespace Sqids.Benchmarks;
+
+[MemoryDiagnoser]
+public class EncodeBenchmark
+{
+#if NET7_0_OR_GREATER
+	private SqidsEncoder<int> _encoder = new SqidsEncoder<int>();
+#else
+	private SqidsEncoder _encoder = new SqidsEncoder();
+#endif
+
+	[Benchmark]
+	public string EncodeSmall() => _encoder.Encode(42);
+
+	[Benchmark]
+	public string EncodeBig() => _encoder.Encode(int.MaxValue);
+
+	[Benchmark]
+	public string EncodeMany() => _encoder.Encode(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+	[Benchmark]
+	public IReadOnlyList<int> DecodeSmall() => _encoder.Decode("Jg");
+
+	[Benchmark]
+	public IReadOnlyList<int> DecodeBig() => _encoder.Decode("UKrsQ1F");
+
+	[Benchmark]
+	public IReadOnlyList<int> DecodeMany() => _encoder.Decode("hwB5vcCxfAyBnVKMtAaV");
+}

benchmark/Sqids.Benchmarks/Program.cs

@@ -0,0 +1,20 @@
+using BenchmarkDotNet.Configs;
+using BenchmarkDotNet.Environments;
+using BenchmarkDotNet.Jobs;
+using BenchmarkDotNet.Running;
+
+namespace Sqids.Benchmarks;
+
+public static class Program
+{
+	public static void Main(string[] args)
+	{
+		IConfig config = ManualConfig.CreateMinimumViable()
+			.AddJob(Job.Default.WithRuntime(ClrRuntime.Net472))
+			.AddJob(Job.Default.WithRuntime(CoreRuntime.Core60))
+			.AddJob(Job.Default.WithRuntime(CoreRuntime.Core70))
+			.AddJob(Job.Default.WithRuntime(CoreRuntime.Core80));
+
+		BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args, config);
+	}
+}

benchmark/Sqids.Benchmarks/Sqids.Benchmarks.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+	<PropertyGroup>
+		<!-- NOTE: `net472` is used for testing `netstandard2.0` -->
+		<TargetFrameworks>net472;net6.0;net7.0;net8.0</TargetFrameworks>
+		<LangVersion>12.0</LangVersion>
+		<ImplicitUsings>enable</ImplicitUsings>
+		<Nullable>enable</Nullable>
+		<OutputType>exe</OutputType>
+	</PropertyGroup>
+
+	<ItemGroup>
+		<ProjectReference Include="..\..\src\Sqids\Sqids.csproj" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <PackageReference Include="BenchmarkDotNet" Version="0.13.12" />
+	</ItemGroup>
+
+</Project>

src/Sqids/SqidsEncoder.cs

@@ -1,5 +1,7 @@
+using System.Runtime.CompilerServices;
 #if NET7_0_OR_GREATER
 using System.Numerics;
+using System.Runtime.CompilerServices;
 #endif
 
 namespace Sqids;
@@ -71,13 +73,13 @@ public SqidsEncoder(SqidsOptions options)
 
 		if (options.Alphabet.Distinct().Count() != options.Alphabet.Length)
 			throw new ArgumentOutOfRangeException(
-				nameof(options.MinLength),
+				nameof(options.Alphabet),
 				"The alphabet must not contain duplicate characters."
 			);
 
 		if (Encoding.UTF8.GetByteCount(options.Alphabet) != options.Alphabet.Length)
 			throw new ArgumentOutOfRangeException(
-				nameof(options.MinLength),
+				nameof(options.Alphabet),
 				"The alphabet must not contain multi-byte characters."
 			);
 
@@ -96,21 +98,28 @@ public SqidsEncoder(SqidsOptions options)
 		_minLength = options.MinLength;
 
 		// NOTE: Cleanup the blocklist:
-		options.BlockList = new HashSet<string>(
-			options.BlockList,
+		HashSet<string> blockList = new HashSet<string>(
 			StringComparer.OrdinalIgnoreCase // NOTE: Effectively removes items that differ only in casing — leaves one version of each word casing-wise which will then be compared against the generated IDs case-insensitively
 		);
-		options.BlockList.RemoveWhere(w =>
-			// NOTE: Removes words that are less than 3 characters long
-			w.Length < 3 ||
-			// NOTE: Removes words that contain characters not found in the alphabet
+
+		foreach (string w in options.BlockList)
+		{
+			if (
+				// NOTE: Removes words that are less than 3 characters long
+				w.Length < 3 ||
+				// NOTE: Removes words that contain characters not found in the alphabet
 #if NETSTANDARD2_0
-			w.Any(c => options.Alphabet.IndexOf(c.ToString(), StringComparison.OrdinalIgnoreCase) == -1) // NOTE: A `string.Contains` overload with `StringComparison` didn't exist prior to .NET Standard 2.1, so we have to resort to `IndexOf` — see https://stackoverflow.com/a/52791476
+				w.Any(c => options.Alphabet.IndexOf(c.ToString(), StringComparison.OrdinalIgnoreCase) == -1) // NOTE: A `string.Contains` overload with `StringComparison` didn't exist prior to .NET Standard 2.1, so we have to resort to `IndexOf` — see https://stackoverflow.com/a/52791476
 #else
-			w.Any(c => !options.Alphabet.Contains(c, StringComparison.OrdinalIgnoreCase))
+				w.Any(c => !options.Alphabet.Contains(c, StringComparison.OrdinalIgnoreCase))
 #endif
-		);
-		_blockList = [.. options.BlockList]; // NOTE: Arrays are faster to iterate than HashSets, so we construct an array here.
+				)
+				continue;
+
+			blockList.Add(w);
+		}
+
+		_blockList = blockList.ToArray(); // NOTE: Arrays are faster to iterate than HashSets, so we construct an array here.
 
 		_alphabet = options.Alphabet.ToCharArray();
 		ConsistentShuffle(_alphabet);
@@ -231,12 +240,14 @@ private string Encode(ReadOnlySpan<int> numbers, int increment = 0)
 		var builder = new StringBuilder(); // TODO: pool a la Hashids.net?
 		builder.Append(prefix);
 
+		Span<char> idBuffer = stackalloc char[64]; //NOTE: The smallest alphabet (3 chars) with the largest value (ulong.MaxValue) needs 64 bytes
+
 		for (int i = 0; i < numbers.Length; i++)
 		{
 			var number = numbers[i];
 			var alphabetWithoutSeparator = alphabetTemp[1..]; // NOTE: Excludes the first character — which is the separator
-			var encodedNumber = ToId(number, alphabetWithoutSeparator);
-			builder.Append(encodedNumber);
+			int written = ToId(number, alphabetWithoutSeparator, idBuffer);
+			builder.Append(idBuffer[^written..]); // NOTE: The buffer is written from the end towards the beginning
 
 			if (i >= numbers.Length - 1) // NOTE: If the last one
 				continue;
@@ -387,29 +398,34 @@ private static void ConsistentShuffle(Span<char> chars)
 	}
 
 #if NET7_0_OR_GREATER
-	private static ReadOnlySpan<char> ToId(T num, ReadOnlySpan<char> alphabet)
+	private static int ToId(T num, ReadOnlySpan<char> alphabet, Span<char> buffer)
 #else
-	private static ReadOnlySpan<char> ToId(int num, ReadOnlySpan<char> alphabet)
+	private static int ToId(int num, ReadOnlySpan<char> alphabet, Span<char> buffer)
 #endif
 	{
-		var id = new StringBuilder();
-		var result = num;
+		int offset = buffer.Length - 1; // NOTE: Start at the end of the buffer
+
+#if NET7_0_OR_GREATER
+		T alphaLen = T.CreateChecked(alphabet.Length);
+#else
+		int alphaLen = alphabet.Length;
+#endif
 
 #if NET7_0_OR_GREATER
 		do
 		{
-			id.Insert(0, alphabet[int.CreateChecked(result % T.CreateChecked(alphabet.Length))]);
-			result /= T.CreateChecked(alphabet.Length);
-		} while (result > T.Zero);
+			buffer[offset--] = alphabet[int.CreateChecked(num % alphaLen)];
+			num /= alphaLen;
+		} while (num > T.Zero);
 #else
 		do
 		{
-			id.Insert(0, alphabet[result % alphabet.Length]);
-			result /= alphabet.Length;
-		} while (result > 0);
+			buffer[offset--] = alphabet[num % alphaLen];
+			num /= alphaLen;
+		} while (num > 0);
 #endif
-
-		return id.ToString().AsSpan(); // TODO: possibly avoid creating a string
+		// NOTE: Return how much we have written back to the caller
+		return buffer.Length - offset - 1;
 	}
 
 #if NET7_0_OR_GREATER