From 21f2b5e1db1a118c83a3690055c110d0f5637da3 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 10 Aug 2021 18:38:41 +0300
Subject: [PATCH] Fix hash_combine_impl to only test for a specific bit width
 and not for concrete types

---
 include/boost/container_hash/hash.hpp | 75 ++++++++++++++-------------
 1 file changed, 40 insertions(+), 35 deletions(-)

diff --git a/include/boost/container_hash/hash.hpp b/include/boost/container_hash/hash.hpp
index 6059fee..06fa8a3 100644
--- a/include/boost/container_hash/hash.hpp
+++ b/include/boost/container_hash/hash.hpp
@@ -26,6 +26,7 @@
 #include <boost/type_traits/is_integral.hpp>
 #include <boost/core/enable_if.hpp>
 #include <boost/cstdint.hpp>
+#include <climits>
 
 #if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
 #include <boost/type_traits/is_pointer.hpp>
@@ -307,52 +308,56 @@ namespace boost
              return seed;
         }
 
-        template <typename SizeT>
-        inline void hash_combine_impl(SizeT& seed, SizeT value)
+        template<int Bits> struct hash_combine_impl
         {
-            seed ^= value + 0x9e3779b9 + (seed<<6) + (seed>>2);
-        }
+            template <typename SizeT>
+            inline static SizeT fn(SizeT seed, SizeT value)
+            {
+                seed ^= value + 0x9e3779b9 + (seed<<6) + (seed>>2);
+                return seed;
+            }
+        };
 
-        inline void hash_combine_impl(boost::uint32_t& h1,
-                boost::uint32_t k1)
+        template<> struct hash_combine_impl<32>
         {
-            const uint32_t c1 = 0xcc9e2d51;
-            const uint32_t c2 = 0x1b873593;
+            inline static boost::uint32_t fn(boost::uint32_t h1, boost::uint32_t k1)
+            {
+                const boost::uint32_t c1 = 0xcc9e2d51;
+                const boost::uint32_t c2 = 0x1b873593;
 
-            k1 *= c1;
-            k1 = BOOST_FUNCTIONAL_HASH_ROTL32(k1,15);
-            k1 *= c2;
+                k1 *= c1;
+                k1 = BOOST_FUNCTIONAL_HASH_ROTL32(k1,15);
+                k1 *= c2;
 
-            h1 ^= k1;
-            h1 = BOOST_FUNCTIONAL_HASH_ROTL32(h1,13);
-            h1 = h1*5+0xe6546b64;
-        }
+                h1 ^= k1;
+                h1 = BOOST_FUNCTIONAL_HASH_ROTL32(h1,13);
+                h1 = h1*5+0xe6546b64;
 
+                return h1;
+            }
+        };
 
-// Don't define 64-bit hash combine on platforms without 64 bit integers,
-// and also not for 32-bit gcc as it warns about the 64-bit constant.
-#if !defined(BOOST_NO_INT64_T) && \
-        !(defined(__GNUC__) && ULONG_MAX == 0xffffffff)
-
-        inline void hash_combine_impl(boost::uint64_t& h,
-                boost::uint64_t k)
+        template<> struct hash_combine_impl<64>
         {
-            const boost::uint64_t m = UINT64_C(0xc6a4a7935bd1e995);
-            const int r = 47;
+            inline static boost::uint64_t fn(boost::uint64_t h, boost::uint64_t k)
+            {
+                const boost::uint64_t m = (boost::uint64_t(0xc6a4a793) << 32) + 0x5bd1e995;
+                const int r = 47;
 
-            k *= m;
-            k ^= k >> r;
-            k *= m;
+                k *= m;
+                k ^= k >> r;
+                k *= m;
 
-            h ^= k;
-            h *= m;
+                h ^= k;
+                h *= m;
 
-            // Completely arbitrary number, to prevent 0's
-            // from hashing to 0.
-            h += 0xe6546b64;
-        }
+                // Completely arbitrary number, to prevent 0's
+                // from hashing to 0.
+                h += 0xe6546b64;
 
-#endif // BOOST_NO_INT64_T
+                return h;
+            }
+        };
     }
 
     template <typename T>
@@ -413,7 +418,7 @@ namespace boost
     inline void hash_combine(std::size_t& seed, T const& v)
     {
         boost::hash<T> hasher;
-        return boost::hash_detail::hash_combine_impl(seed, hasher(v));
+        seed = boost::hash_detail::hash_combine_impl<sizeof(std::size_t) * CHAR_BIT>::fn(seed, hasher(v));
     }
 
 #if defined(BOOST_MSVC)