Hash utility functions (#385)

* added std::hash implementation for Guid and Oid types
* Added CombineHashes implementation

3 files changed, 51 insertions, 0 deletions

diff --git a/src/zencore/include/zencore/guid.h b/src/zencore/include/zencore/guid.h
index 751aa945f..13e1b5540 100644
--- a/src/zencore/include/zencore/guid.h
+++ b/src/zencore/include/zencore/guid.h
@@ -2,7 +2,9 @@
 
 #pragma once
 
+#include <zencore/hashutils.h>
 #include <zencore/zencore.h>
+
 #include <compare>
 
 namespace zen {
@@ -24,3 +26,9 @@ struct Guid
 };
 
 }  // namespace zen
+
+template<>
+struct std::hash<zen::Guid>
+{
+	std::size_t operator()(const zen::Guid& In) const noexcept { return zen::CombineHashes(In.A, In.B, In.C, In.D); }
+};
diff --git a/src/zencore/include/zencore/hashutils.h b/src/zencore/include/zencore/hashutils.h
new file mode 100644
index 000000000..4e877e219
--- /dev/null
+++ b/src/zencore/include/zencore/hashutils.h
@@ -0,0 +1,34 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#pragma once
+
+namespace zen {
+
+template<typename T>
+void
+_CombineHashes(size_t& Seed, const T& Val)
+{
+	Seed ^= std::hash<T>()(Val) + 0x9e3779b97f4a7c15ull + (Seed << 12) + (Seed >> 4);
+}
+
+/** Utility function to generate a high quality hash from multiple
+	contributing items
+
+	Example usage:
+
+		const Guid A = GetA();
+		const std::string B = GetB();
+
+		const size_t AbHash = CombineHashes(A, B);
+
+ */
+template<typename... Types>
+size_t
+CombineHashes(const Types&... Args)
+{
+	size_t Seed = 0;
+	(_CombineHashes(Seed, Args), ...);
+	return Seed;
+}
+
+}  // namespace zen
diff --git a/src/zencore/include/zencore/uid.h b/src/zencore/include/zencore/uid.h
index 4a1285416..557567473 100644
--- a/src/zencore/include/zencore/uid.h
+++ b/src/zencore/include/zencore/uid.h
@@ -85,3 +85,12 @@ struct Oid
 extern void uid_forcelink();
 
 }  // namespace zen
+
+namespace std {
+
+template<>
+struct hash<zen::Oid> : public zen::Oid::Hasher
+{
+};
+
+}  // namespace std