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Overview

src/Common is not a compiled project. It contains no .csproj, no AssemblyInfo, and no NuGet package manifest. Instead it is a bare source-file directory used as a solution-folder grouping in several Visual Studio solution files (NuGet.Jobs.sln, NuGet.Jobs.FunctionalTests.sln). Its only current content is a single .cs file that was copied verbatim from the retired ASP.NET Web Stack CodePlex repository and is licensed under the Apache 2.0 License. The file that lives here — HashCodeCombiner.cs — provides a small, stateful hash-accumulator class. It uses the djb2 polynomial rolling-hash algorithm (hash = (hash << 5) + hash ^ value) seeded at 0x1505 to combine the hash codes of arbitrarily many objects, integers, or collections into a single int. Because the class is declared internal, any project that needs it must either include this file directly as a linked source item, or copy it locally. The namespace was deliberately changed from the original Microsoft namespace to NuGet.Services so that callers in the NuGet Gallery source tree can use the type without adding an extra using directive.

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Role in System

src/Common/
└── HashCodeCombiner.cs    ← single vendored utility file
                              namespace: NuGet.Services
                              visibility: internal
                              license: Apache 2.0 (copied from aspnetwebstack)

Solution folder membership
  NuGet.Jobs.sln              → "Common" folder (solution-organizer only)
  NuGet.Jobs.FunctionalTests.sln → "Common" folder (solution-organizer only)
The directory has no compile-time presence of its own. Projects that need HashCodeCombiner must reference the file explicitly (e.g., via a <Compile Include="..." Link="..."> item in their .csproj). There are no .csproj-level references to this directory currently active in the repository.

Vendored Utility

HashCodeCombiner.cs is a verbatim copy of a file from the retired aspnetwebstack CodePlex project, retained under its original Apache 2.0 license. No modifications were made to the algorithm; only the namespace was changed.

No Build Artifact

The directory produces no .dll, NuGet package, or other build output. It is a source-sharing mechanism only, organized as a solution folder in Visual Studio rather than as a standalone C# project.

djb2 Hash Algorithm

The combiner seeds at 0x1505 and accumulates values using hash = (hash << 5) + hash ^ value, the classic djb2 polynomial variant. The final int result is obtained by calling .GetHashCode() on the internal long accumulator.

Fluent Builder API

All Add overloads return this, enabling a fluent chain: HashCodeCombiner.Start().Add(a).Add(b).CombinedHash. Null objects and null enumerables are handled gracefully (treated as hash value 0).

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Key Files and Classes

FileClass / TypePurpose
HashCodeCombiner.csHashCodeCombiner (internal)Accumulates hash codes for multiple objects, integers, or IEnumerable sequences into a single combined int using the djb2 polynomial algorithm. Provides a static Start() factory and fluent Add overloads.

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Dependencies

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NuGet Package References

None. The directory contains no project file and declares no package dependencies.

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Internal Project References

None. src/Common is not a project; it carries no <ProjectReference> entries.

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Notable Patterns and Implementation Details

Not a compilable project. src/Common has no .csproj file. It appears in solution files purely as a Visual Studio solution folder for organizational grouping. The directory cannot be built independently with dotnet build or msbuild.
Namespace intentionally changed from the original. The file comment explicitly states: “Namespace changed from original to avoid requiring using statements.” The class lives in NuGet.Services rather than in any Microsoft-owned namespace so that consuming code in the NuGet.Services.* project tree can use it without an extra using directive.
internal visibility limits reuse. HashCodeCombiner is declared internal, meaning it is only accessible within the same assembly. Any project that needs this class must either link the file directly in its .csproj or copy it locally. There is currently no linked-file reference to this directory in the repository’s active .csproj files, suggesting the type may be unused at present or has been superseded by System.HashCode (available since .NET Standard 2.1 / .NET Core 2.1).
Enumerables include element count in the hash. When hashing an IEnumerable, the combiner iterates all elements and then also hashes the total count. This means two sequences with the same elements in the same order but different lengths (which is impossible for a valid IEnumerable) are guaranteed different, and it prevents hash collisions between prefix sequences.