Add xmx2_mix

include/boost/unordered/detail/foa.hpp

@@ -761,6 +761,15 @@ struct xmx_mix
   }
 };
 
+struct xmx2_mix
+{
+  template<typename Hash,typename T>
+  static inline std::size_t mix(const Hash& h,const T& x)
+  {
+    return xmx2(h(x));
+  }
+};
+
 struct mulx_mix
 {
   template<typename Hash,typename T>

include/boost/unordered/detail/xmx.hpp

@@ -64,6 +64,31 @@ static inline std::size_t xmx(std::size_t x)noexcept
 #endif
 }
 
+// alternative multipliers
+
+static inline std::size_t xmx2( std::size_t x ) noexcept
+{
+#if defined(BOOST_UNORDERED_64B_ARCHITECTURE)
+
+  boost::uint64_t z=(boost::uint64_t)x;
+
+  z ^= z >> 23;
+  z *= 0x9E3779B97F4A7C15ull;
+  z ^= z >> 23;
+
+  return (std::size_t)z;
+
+#else /* 32 bits assumed */
+
+  x ^= x >> 18;
+  x *= 0x9E3779B9u;
+  x ^= x >> 16;
+
+  return x;
+
+#endif
+}
+
 #ifdef BOOST_UNORDERED_64B_ARCHITECTURE
 #undef BOOST_UNORDERED_64B_ARCHITECTURE
 #endif