From 7040c57750e97fd1b09ac39ca6222ad915ec8de8 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Thu, 8 Dec 2022 21:40:13 +0200
Subject: [PATCH] Add mulx_mix

---
 include/boost/unordered/detail/foa.hpp  |  10 ++
 include/boost/unordered/detail/mulx.hpp | 118 ++++++++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 include/boost/unordered/detail/mulx.hpp

diff --git a/include/boost/unordered/detail/foa.hpp b/include/boost/unordered/detail/foa.hpp
index 89d79dae..289ea457 100644
--- a/include/boost/unordered/detail/foa.hpp
+++ b/include/boost/unordered/detail/foa.hpp
@@ -23,6 +23,7 @@
 #include <boost/predef.h>
 #include <boost/type_traits/is_nothrow_swappable.hpp>
 #include <boost/unordered/detail/xmx.hpp>
+#include <boost/unordered/detail/mulx.hpp>
 #include <boost/unordered/hash_traits.hpp>
 #include <climits>
 #include <cmath>
@@ -760,6 +761,15 @@ struct xmx_mix
   }
 };
 
+struct mulx_mix
+{
+  template<typename Hash,typename T>
+  static inline std::size_t mix(const Hash& h,const T& x)
+  {
+    return mulx(h(x));
+  }
+};
+
 /* boost::core::countr_zero has a potentially costly check for
  * the case x==0.
  */
diff --git a/include/boost/unordered/detail/mulx.hpp b/include/boost/unordered/detail/mulx.hpp
new file mode 100644
index 00000000..93baea9f
--- /dev/null
+++ b/include/boost/unordered/detail/mulx.hpp
@@ -0,0 +1,118 @@
+#ifndef BOOST_UNORDERED_DETAIL_MULX_HPP
+#define BOOST_UNORDERED_DETAIL_MULX_HPP
+
+// Copyright 2022 Peter Dimov.
+// Copyright 2022 Joaquin M Lopez Munoz.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/cstdint.hpp>
+#include <climits>
+#include <cstddef>
+
+#if defined(_MSC_VER) && !defined(__clang__)
+# include <intrin.h>
+#endif
+
+namespace boost {
+namespace unordered {
+namespace detail {
+
+// Bit mixer based on the mulx primitive
+
+#if defined(_MSC_VER) && defined(_M_X64) && !defined(__clang__)
+
+__forceinline boost::uint64_t mulx64( boost::uint64_t x, boost::uint64_t y )
+{
+    boost::uint64_t r2;
+    boost::uint64_t r = _umul128( x, y, &r2 );
+    return r ^ r2;
+}
+
+#elif defined(_MSC_VER) && defined(_M_ARM64) && !defined(__clang__)
+
+__forceinline boost::uint64_t mulx64( boost::uint64_t x, boost::uint64_t y )
+{
+    boost::uint64_t r = x * y;
+    boost::uint64_t r2 = __umulh( x, y );
+    return r ^ r2;
+}
+
+#elif defined(__SIZEOF_INT128__)
+
+inline boost::uint64_t mulx64( boost::uint64_t x, boost::uint64_t y )
+{
+    __uint128_t r = (__uint128_t)x * y;
+    return (boost::uint64_t)r ^ (boost::uint64_t)( r >> 64 );
+}
+
+#else
+
+inline boost::uint64_t mulx64( boost::uint64_t x, boost::uint64_t y )
+{
+    boost::uint64_t x1 = (boost::uint32_t)x;
+    boost::uint64_t x2 = x >> 32;
+
+    boost::uint64_t y1 = (boost::uint32_t)y;
+    boost::uint64_t y2 = y >> 32;
+
+    boost::uint64_t r3 = x2 * y2;
+
+    boost::uint64_t r2a = x1 * y2;
+
+    r3 += r2a >> 32;
+
+    boost::uint64_t r2b = x2 * y1;
+
+    r3 += r2b >> 32;
+
+    boost::uint64_t r1 = x1 * y1;
+
+    boost::uint64_t r2 = (r1 >> 32) + (boost::uint32_t)r2a + (boost::uint32_t)r2b;
+
+    r1 = (r2 << 32) + (boost::uint32_t)r1;
+    r3 += r2 >> 32;
+
+    return r1 ^ r3;
+}
+
+#endif
+
+inline boost::uint32_t mulx32( boost::uint32_t x, boost::uint32_t y )
+{
+    boost::uint64_t r = (boost::uint64_t)x * y;
+    return (boost::uint32_t)r ^ (boost::uint32_t)(r >> 32);
+}
+
+#if defined(SIZE_MAX)
+#if ((((SIZE_MAX >> 16) >> 16) >> 16) >> 15) != 0
+#define BOOST_UNORDERED_64B_ARCHITECTURE /* >64 bits assumed as 64 bits */
+#endif
+#elif defined(UINTPTR_MAX) /* used as proxy for std::size_t */
+#if ((((UINTPTR_MAX >> 16) >> 16) >> 16) >> 15) != 0
+#define BOOST_UNORDERED_64B_ARCHITECTURE
+#endif
+#endif
+
+inline std::size_t mulx( std::size_t x ) noexcept
+{
+#if defined(BOOST_UNORDERED_64B_ARCHITECTURE)
+
+    return (std::size_t)mulx64( (boost::uint64_t)x, 0x9E3779B97F4A7C15ull );
+
+#else /* 32 bits assumed */
+
+    return mulx32( x, 0x9E3779B9u );
+
+#endif
+}
+
+#ifdef BOOST_UNORDERED_64B_ARCHITECTURE
+#undef BOOST_UNORDERED_64B_ARCHITECTURE
+#endif
+
+} // namespace detail
+} // namespace unordered
+} // namespace boost
+
+#endif // #ifndef BOOST_UNORDERED_DETAIL_MULX_HPP