Add CoPilot instructions

Author: walbourn

.github/copilot-instructions.md

@@ -0,0 +1,85 @@
+# GitHub Copilot Instructions
+
+These instructions define how GitHub Copilot should assist with this project. The goal is to ensure consistent, high-quality code generation aligned with our conventions, stack, and best practices.
+
+## Context
+
+- **Project Type**: Math Library / DirectX / Direct3D
+- **Project Name**: DirectXMath SIMD C++ linear algebra library
+- **Language**: C++
+- **Framework / Libraries**: STL / CMake / CTest
+
+## Getting Started
+
+- See the Getting Started guide on [Microsoft Learn](https://learn.microsoft.com/windows/win32/dxmath/pg-xnamath-getting-started).
+- The recommended way to integrate *DirectXMath* into your project is by using the *vcpkg* Package Manager.
+- You can make use of the nuget.org package **directxmath**.
+- You can also use the library source code directly in your project or as a git submodule.
+- The Windows SDK includes the DirectXMath library, although that version is not as up-to-date as other integration methods.
+
+## General Guidelines
+
+- **Code Style**: The project uses an .editorconfig file to enforce coding standards. Follow the rules defined in `.editorconfig` for indentation, line endings, and other formatting. Additional information can be found on the wiki at [Implementation](https://github.com/microsoft/DirectXMath/wiki/Implementation). The code requires C++11/C++14 features.
+- **Documentation**: The project provides documentation on [Microsoft Learn](https://learn.microsoft.com/windows/win32/dxmath/directxmath-portal) with additional wiki pages available on [GitHub](https://github.com/microsoft/DirectXMath/wiki/).
+- **Error Handling**: The majority of functions have no error conditions and do not throw C++ exceptions which is why they are marked `noexcept`. A few functions have `bool` results to indicate success or failure.
+- **Testing**: Unit tests for this project are implemented in this repository [Test Suite](https://github.com/walbourn/directxmathtest/) and can be run using CTest per the instructions at [Test Documentation](https://github.com/walbourn/directxmathtest/wiki).
+- **Security**: This project uses secure coding practices from the Microsoft Secure Coding Guidelines, and is subject to the `SECURITY.md` file in the root of the repository.
+- **Dependencies**: The project has minimal dependencies, primarily relying on compiler intrinsics. It is designed to be self-contained and portable across different platforms and toolsets.
+- **Continuous Integration**: This project implements GitHub Actions for continuous integration, ensuring that all code changes are tested and validated before merging. This includes building the project for a number of configurations and toolsets, running unit tests, and static code analysis including GitHub super-linter, CodeQL, and MSVC Code Analysis.
+- **Code of Conduct**: The project adheres to the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). All contributors are expected to follow this code of conduct in all interactions related to the project.
+
+## File Structure
+
+```txt
+.azuredevops/ # Azure DevOps pipeline configuration and policy files.
+.github/      # GitHub Actions workflow files and linter configuration files.
+.nuget/       # NuGet package configuration files.
+build/        # Miscellaneous build files and scripts.
+Inc/          # DirectXMath public and implementation files. The library is header-only, so all files are in this directory.
+Extensions/   # Extensions to the DirectXMath library with standalone SSE-level specific functions for runtime selection of SIMD instruction set.
+MatrixStack/  # D3DX9-like matrix stack implementation for DirectXMath.
+SHMath/       # Spherical harmonic functions using DirectXMath.
+Stereo3D/     # Stereo 3D projection matrix functions using DirectXMath created for HoloLens.
+XDSP/         # Digital Signal Processing (DSP) functions using DirectXMath.
+Tests/        # Tests are designed to be cloned from a separate repository at this location.
+```
+
+> The `Extensions` are not needed if building the library using `/arch:AVX` or `/arch:AVX2` which causes the DirectXMath library to build utilizing the additional SIMD instructions.
+
+## References
+
+- [C++ Core Guidelines](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines)
+- [Microsoft Secure Coding Guidelines](https://learn.microsoft.com/en-us/security/develop/secure-coding-guidelines)
+- [CMake Documentation](https://cmake.org/documentation/)
+- [VCPK Documentation](https://learn.microsoft.com/vcpkg/)
+- [DirectXMath Documentation](https://learn.microsoft.com/windows/win32/dxmath/directxmath-portal)
+- [DirectXMath Wiki](https://github.com/microsoft/DirectXMath/wiki/)
+- [Games for Windows and the DirectX SDK blog - March 2012](https://walbourn.github.io/introducing-directxmath/)
+
+## No speculation
+
+When creating documentation:
+
+### Document Only What Exists
+
+- Only document features, patterns, and decisions that are explicitly present in the source code.
+- Only include configurations and requirements that are clearly specified.
+- Do not make assumptions about implementation details.
+
+### Handle Missing Information
+
+- Ask the user questions to gather missing information.
+- Document gaps in current implementation or specifications.
+- List open questions that need to be addressed.
+
+### Source Material
+
+- Always cite the specific source file and line numbers for documented features.
+- Link directly to relevant source code when possible.
+- Indicate when information comes from requirements vs. implementation.
+
+### Verification Process
+
+- Review each documented item against source code whenever related to the task.
+- Remove any speculative content.
+- Ensure all documentation is verifiable against the current state of the codebase.