basic arithmetic benchmarks added

.gitea/workflows/test-dotnet.yaml

@@ -49,6 +49,11 @@ jobs:
         --report-xunit-trx --coverlet --coverlet-output-format cobertura
         --coverlet-include "[Just.PreciseMath]*"
 
+    - name: Benchmark smoke test
+      run: >-
+        dotnet run --project 2-benchmarks/Just.PreciseMath.Benchmarks
+        --configuration Release --no-build -- --job Dry --filter '*'
+
     - name: Upload test and coverage results
       uses: actions/upload-artifact@v7
       if: ${{ always() }}

2-benchmarks/Just.PreciseMath.Benchmarks/ArithmeticBenchmarks.cs

@@ -0,0 +1,107 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Configs;
+
+namespace Just.PreciseMath.Benchmarks;
+
+/// <summary>Compares same-type scalar arithmetic on ordinary finite operands.</summary>
+[MemoryDiagnoser]
+[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
+[CategoriesColumn]
+public class ArithmeticBenchmarks
+{
+    private double _doubleLeft;
+    private double _doubleRight;
+    private decimal _decimalLeft;
+    private decimal _decimalRight;
+    private DoubleDouble _doubleDoubleLeft;
+    private DoubleDouble _doubleDoubleRight;
+
+    /// <summary>One binary-exact input and one decimal input with a binary residual.</summary>
+    [Params(1.25, 1.1)]
+    public double Left { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        // Conversion and construction are deliberately outside the timed methods.
+        // Decimal and DoubleDouble represent the same decimal input; double rounds it.
+        _doubleLeft = Left;
+        _doubleRight = 0.75;
+        _decimalLeft = (decimal)Left;
+        _decimalRight = 0.75m;
+        _doubleDoubleLeft = (DoubleDouble)_decimalLeft;
+        _doubleDoubleRight = (DoubleDouble)_decimalRight;
+    }
+
+    [Benchmark(Baseline = true), BenchmarkCategory("Addition")]
+    public double DoubleAdd()
+    {
+        return _doubleLeft + _doubleRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Addition")]
+    public decimal DecimalAdd()
+    {
+        return _decimalLeft + _decimalRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Addition")]
+    public DoubleDouble DoubleDoubleAdd()
+    {
+        return _doubleDoubleLeft + _doubleDoubleRight;
+    }
+
+    [Benchmark(Baseline = true), BenchmarkCategory("Subtraction")]
+    public double DoubleSubtract()
+    {
+        return _doubleLeft - _doubleRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Subtraction")]
+    public decimal DecimalSubtract()
+    {
+        return _decimalLeft - _decimalRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Subtraction")]
+    public DoubleDouble DoubleDoubleSubtract()
+    {
+        return _doubleDoubleLeft - _doubleDoubleRight;
+    }
+
+    [Benchmark(Baseline = true), BenchmarkCategory("Multiplication")]
+    public double DoubleMultiply()
+    {
+        return _doubleLeft * _doubleRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Multiplication")]
+    public decimal DecimalMultiply()
+    {
+        return _decimalLeft * _decimalRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Multiplication")]
+    public DoubleDouble DoubleDoubleMultiply()
+    {
+        return _doubleDoubleLeft * _doubleDoubleRight;
+    }
+
+    [Benchmark(Baseline = true), BenchmarkCategory("Division")]
+    public double DoubleDivide()
+    {
+        return _doubleLeft / _doubleRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Division")]
+    public decimal DecimalDivide()
+    {
+        return _decimalLeft / _decimalRight;
+    }
+
+    [Benchmark, BenchmarkCategory("Division")]
+    public DoubleDouble DoubleDoubleDivide()
+    {
+        return _doubleDoubleLeft / _doubleDoubleRight;
+    }
+}

2-benchmarks/Just.PreciseMath.Benchmarks/Just.PreciseMath.Benchmarks.csproj

@@ -2,9 +2,8 @@
   <PropertyGroup>
     <AssemblyName>Just.PreciseMath.Benchmarks</AssemblyName>
     <RootNamespace>Just.PreciseMath.Benchmarks</RootNamespace>
-    <Description>BenchmarkDotNet scaffold for measuring Just.PreciseMath arithmetic and mathematical functions.</Description>
-    <!-- Source-free scaffold: change to Exe when adding the benchmark entry point. -->
-    <OutputType>Library</OutputType>
+    <Description>BenchmarkDotNet comparisons of DoubleDouble, decimal, and double arithmetic.</Description>
+    <OutputType>Exe</OutputType>
   </PropertyGroup>
 
   <ItemGroup>

2-benchmarks/Just.PreciseMath.Benchmarks/Program.cs

@@ -0,0 +1,31 @@
+using BenchmarkDotNet.Reports;
+using BenchmarkDotNet.Running;
+
+namespace Just.PreciseMath.Benchmarks;
+
+internal static class Program
+{
+    private static int Main(string[] args)
+    {
+        BenchmarkSwitcher switcher = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly);
+        // Only these standalone discovery/help forms intentionally produce no reports.
+        if (args is ["--list", "flat" or "tree"] or ["--help"] or ["-h"])
+        {
+            switcher.Run(args);
+            return 0;
+        }
+
+        Summary[] summaries = switcher.Run(args.Length == 0 ? ["--filter", "*"] : args).ToArray();
+        // BenchmarkDotNet can return normally after validation, build, or execution
+        // failures. Do not let CI mistake an empty or failed run for a passing smoke test.
+        if (summaries.Length == 0 || summaries.Any(summary =>
+            summary.HasCriticalValidationErrors || summary.Reports.Length == 0 ||
+            summary.Reports.Any(report => !report.Success || report.ResultStatistics is null)))
+        {
+            Console.Error.WriteLine("Benchmark run failed or produced no measurements.");
+            return 1;
+        }
+
+        return 0;
+    }
+}

AGENTS.md

@@ -12,8 +12,8 @@ Do not claim API completeness or accuracy beyond tested contracts.
 - `0-source/Just.PreciseMath/`: library implementation and package metadata.
 - `1-tests/Just.PreciseMath.Tests/`: xUnit v3 tests, Shouldly assertions, and
   Microsoft.Testing.Platform (MTP) with `coverlet.MTP` coverage.
-- `2-benchmarks/Just.PreciseMath.Benchmarks/`: source-free BenchmarkDotNet library
-  scaffold, not yet a runnable benchmark suite.
+- `2-benchmarks/Just.PreciseMath.Benchmarks/`: executable BenchmarkDotNet arithmetic
+  comparisons; use the Dry job for smoke validation, not performance conclusions.
 - Root `Directory.Build.props` holds shared settings. Each numbered directory's
   props explicitly imports it; preserve this import chain.
 - `review-legacy/`: optional local reference material, excluded by `.gitignore`.

README.md

@@ -42,7 +42,7 @@ rounded 106-bit results**. The deterministic rational-oracle tests check a
 conservative error bound of `2^-100` relative plus one minimum binary64 subnormal,
 with exact component checks for selected representable cases. Near underflow,
 extended precision necessarily decreases; overflow produces infinity. Performance
-has not been benchmarked, including the allocating exponent-boundary path.
+of the allocating exponent-boundary path is not covered by the basic benchmarks.
 
 ## Conversions and formatting
 
@@ -133,8 +133,8 @@ bool success = DoubleDouble.TryParse("1.25e-2".AsSpan(), CultureInfo.InvariantCu
 
 The planned `PreciseMath` static class and its `Abs`, `Sqrt`, `Pow`, `Exp`, and
 `Log` functions are not implemented. Generic-math interfaces beyond `ISignedNumber`,
-additional text formats/general round-trip formatting, and performance benchmarks
-remain deferred.
+additional text formats/general round-trip formatting, and broader performance
+benchmarks remain deferred.
 Replacing allocating arithmetic boundary fallbacks is also deferred; the current
 `BigInteger` paths remain in place. That optimization does not require removing
 `BigInteger` from conversions, parsing, formatting, or independent test oracles.
@@ -154,11 +154,46 @@ dotnet format Just.PreciseMath.slnx --verify-no-changes --no-restore
 Test results and coverage reports are available in the `test-results` artifact
 on CI workflow runs.
 
+## Benchmarks
+
+The BenchmarkDotNet suite compares same-type `+`, `-`, `*`, and `/` operations for
+`DoubleDouble`, `decimal`, and `double`: 12 methods with two input cases each.
+Each operation/input group uses `double` as its baseline and reports allocations.
+Operands are stored in fields and results are returned to the harness; conversions
+and construction happen in setup, outside the timed methods.
+
+The left inputs are `1.25` (binary-exact) and `1.1` (a nonzero low component in
+`DoubleDouble`); the right input is `0.75`. Decimal and double-double inputs originate
+from the same decimal values, while `double` rounds to binary64. These types have
+different precision and range contracts: this is a cost comparison, not an accuracy
+test. Exceptional values, exponent-boundary fallbacks, mixed-type operators,
+conversions, parsing, and formatting are not benchmarked yet.
+
+After the Release build above, run from the repository root:
+
+```sh
+# Discover benchmark methods without running them.
+dotnet run --project 2-benchmarks/Just.PreciseMath.Benchmarks -c Release --no-build -- --list flat
+
+# Quick execution check (also run in CI); not useful for timing comparisons.
+dotnet run --project 2-benchmarks/Just.PreciseMath.Benchmarks -c Release --no-build -- --job Dry --filter '*'
+
+# Full measurement run; optionally select an operation with --anyCategories Addition.
+dotnet run --project 2-benchmarks/Just.PreciseMath.Benchmarks -c Release --no-build -- --filter '*'
+```
+
+Reports are written under the ignored `BenchmarkDotNet.Artifacts/` directory.
+Empty selections and failed benchmark runs return a nonzero exit code. CI only
+checks execution, with no performance gate. Use full runs on an idle, controlled
+machine for comparisons; a scalar `double` operation may approach harness overhead,
+so inspect BenchmarkDotNet warnings before interpreting ratios. Do not compare
+coverage-instrumented runs or treat Dry-job timings as performance measurements.
+
 ## Project structure
 
 - `0-source/Just.PreciseMath/`: library implementation.
 - `1-tests/Just.PreciseMath.Tests/`: unit tests.
-- `2-benchmarks/Just.PreciseMath.Benchmarks/`: reserved for performance benchmarks.
+- `2-benchmarks/Just.PreciseMath.Benchmarks/`: arithmetic benchmarks against `decimal` and `double`.
 
 ## Contributing