First Commit

ext/prometheus-cpp-lite-1.0/core/include/prometheus/hash.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <cstddef>
+#include <functional>
+
+namespace prometheus {
+
+  namespace detail {
+
+    /// \brief Combine a hash value with nothing.
+    /// It's the boundary condition of this serial functions.
+    ///
+    /// \param seed Not effect.
+    inline void hash_combine(std::size_t *) {}
+
+    /// \brief Combine the given hash value with another obeject.
+    ///
+    /// \param seed The given hash value. It's a input/output parameter.
+    /// \param value The object that will be combined with the given hash value.
+    template <typename T>
+    inline void hash_combine(std::size_t *seed, const T &value) {
+      *seed ^= std::hash<T>{}(value) + 0x9e3779b9 + (*seed << 6) + (*seed >> 2);
+    }
+
+    /// \brief Combine the given hash value with another objects. It's a recursion。
+    ///
+    /// \param seed The give hash value. It's a input/output parameter.
+    /// \param value The object that will be combined with the given hash value.
+    /// \param args The objects that will be combined with the given hash value.
+    template <typename T, typename... Types>
+    inline void hash_combine(std::size_t *seed, const T &value,
+                             const Types &...args) {
+      hash_combine(seed, value);
+      hash_combine(seed, args...);
+    }
+
+    /// \brief Compute a hash value of the given args.
+    ///
+    /// \param args The arguments that will be computed hash value.
+    /// \return The hash value of the given args.
+    template <typename... Types>
+    inline std::size_t hash_value(const Types &...args) {
+      std::size_t seed = 0;
+      hash_combine(&seed, args...);
+      return seed;
+    }
+
+  }  // namespace detail
+
+}  // namespace prometheus