From 0d779077c11c0fabce2291237fa503986c61e50b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Leclercq?= <lynix680@gmail.com>
Date: Fri, 30 Oct 2020 23:04:22 +0100
Subject: [PATCH] Core/Algorithm: Add AccessByOffset functions

---
 include/Nazara/Core/Algorithm.hpp |  2 ++
 include/Nazara/Core/Algorithm.inl | 38 +++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/Nazara/Core/Algorithm.hpp b/include/Nazara/Core/Algorithm.hpp
index dec6312a4..6f0754c1b 100644
--- a/include/Nazara/Core/Algorithm.hpp
+++ b/include/Nazara/Core/Algorithm.hpp
@@ -21,6 +21,8 @@ namespace Nz
 {
 	class ByteArray;
 
+	template<typename T> decltype(auto) AccessByOffset(void* basePtr, std::size_t offset);
+	template<typename T> decltype(auto) AccessByOffset(const void* basePtr, std::size_t offset);
 	template<typename T> constexpr T Align(T offset, T alignment);
 	template<typename T> constexpr T AlignPow2(T offset, T alignment);
 	template<typename F, typename Tuple> decltype(auto) Apply(F&& fn, Tuple&& t);
diff --git a/include/Nazara/Core/Algorithm.inl b/include/Nazara/Core/Algorithm.inl
index 3560f775c..3a163cd55 100644
--- a/include/Nazara/Core/Algorithm.inl
+++ b/include/Nazara/Core/Algorithm.inl
@@ -36,6 +36,44 @@ namespace Nz
 		NAZARA_CORE_API extern const UInt8 BitReverseTable256[256];
 	}
 
+	/*!
+	* \ingroup core
+	* \brief Access a non-typed struct field by offset
+	* \return A pointer to the field of the asked type
+	*
+	* \param basePtr Pointer to the start of the struct
+	* \param offset Offset to the field (as generated by offsetof or similar)
+	*/
+	template<typename T>
+	decltype(auto) AccessByOffset(void* basePtr, std::size_t offset)
+	{
+		static_assert((std::is_reference_v<T> && !std::is_rvalue_reference_v<T>) || std::is_pointer_v<T>);
+
+		if constexpr (std::is_reference_v<T>)
+			return *reinterpret_cast<std::remove_reference_t<T>*>(static_cast<Nz::UInt8*>(basePtr) + offset);
+		else
+			return reinterpret_cast<T>(static_cast<Nz::UInt8*>(basePtr) + offset);
+	}
+
+	/*!
+	* \ingroup core
+	* \brief Access a non-typed struct field by offset
+	* \return A pointer to the field of the asked type
+	*
+	* \param basePtr Pointer to the start of the struct
+	* \param offset Offset to the field (as generated by offsetof or similar)
+	*/
+	template<typename T>
+	decltype(auto) AccessByOffset(const void* basePtr, std::size_t offset)
+	{
+		static_assert((std::is_reference_v<T> && !std::is_rvalue_reference_v<T>) || std::is_pointer_v<T>);
+
+		if constexpr (std::is_reference_v<T>)
+			return *reinterpret_cast<std::remove_reference_t<T>*>(static_cast<const Nz::UInt8*>(basePtr) + offset);
+		else
+			return reinterpret_cast<T>(static_cast<const Nz::UInt8*>(basePtr) + offset);
+	}
+
 	/*!
 	* \ingroup core
 	* \brief Align an offset