v01

thirdparty/basalt-headers/include/basalt/utils/hash.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <cstddef>
+
+namespace basalt {
+
+// to work around static_assert(false, ...)
+template <class T>
+struct dependent_false : std::false_type {};
+
+template <class T>
+inline void hash_combine(std::size_t& seed, const T& value) {
+  // Simple hash_combine, see e.g. here:
+  // https://github.com/HowardHinnant/hash_append/issues/7
+  // Not sure we ever need 32bit, but here it is...
+  if constexpr (sizeof(std::size_t) == 4) {
+    seed ^= std::hash<T>{}(value) + 0x9e3779b9U + (seed << 6) + (seed >> 2);
+  } else if constexpr (sizeof(std::size_t) == 8) {
+    seed ^= std::hash<T>{}(value) + 0x9e3779b97f4a7c15LLU + (seed << 12) +
+            (seed >> 4);
+  } else {
+    static_assert(dependent_false<T>::value, "hash_combine not implemented");
+  }
+}
+
+}  // namespace basalt