Factor out hash-combine function

Can be improved separately if folks want to submit PRs
hsutter · Oct 1, 2024 · c5feb42 · c5feb42
1 parent baa6954
commit c5feb42
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Showing 11 changed files with 65 additions and 57 deletions.
diff --git a/include/cpp2util.h b/include/cpp2util.h
@@ -780,6 +780,14 @@ inline auto pointer_eq(T const* a, T const* b) {
     return std::compare_three_way{}(a, b) == std::strong_ordering::equal;
 }
 
+//  PRs welcome to improve this, for suggestions and background see
+//  https://www.boost.org/doc/libs/1_86_0/libs/container_hash/doc/html/hash.html#notes_hash_combine
+inline auto hash_combine(size_t& seed, size_t v) -> void
+{
+    seed ^= v + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+}
+
+
 //-----------------------------------------------------------------------
 //
 //  A type_find_if for iterating over types in parameter packs

diff --git a/regression-tests/test-results/clang-12-c++20/pure2-hashable.cpp.execution b/regression-tests/test-results/clang-12-c++20/pure2-hashable.cpp.execution
@@ -1 +1 @@
-6440649391998984779
+6443762454025613088
diff --git a/regression-tests/test-results/gcc-10-c++20/pure2-default-arguments.cpp.output b/regression-tests/test-results/gcc-10-c++20/pure2-default-arguments.cpp.output
@@ -1,66 +1,66 @@
 In file included from pure2-default-arguments.cpp:7:
 ../../../include/cpp2util.h:2086:28: error: local variable ‘obj’ may not appear in this context
- 2086 | template<typename T, std::same_as<std::any> X>
-      |                            ^~~
+ 2086 | }
+      |                            ^  
 ../../../include/cpp2util.h:2047:34: note: in definition of macro ‘CPP2_UFCS_IDENTITY’
- 2047 |             return false;
+ 2047 |         )
       |                                  ^          
 ../../../include/cpp2util.h:2086:15: note: in expansion of macro ‘CPP2_FORWARD’
- 2086 | template<typename T, std::same_as<std::any> X>
-      |               ^~~~~~~~~~~~
+ 2086 | }
+      |               ^           
 ../../../include/cpp2util.h:2107:22: note: in expansion of macro ‘CPP2_UFCS_CONSTRAINT_ARG’
- 2107 |     }
-      |                      ^                       
+ 2107 |     if constexpr (valid_predicate<decltype(value), decltype(x)>) {
+      |                      ^~~~~~~~~~~~~~~~~~~~~~~~
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 pure2-default-arguments.cpp2:6:22: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 ../../../include/cpp2util.h:2086:92: error: local variable ‘params’ may not appear in this context
- 2086 | template<typename T, std::same_as<std::any> X>
+ 2086 | }
       |                                                                                            ^     
 ../../../include/cpp2util.h:2047:34: note: in definition of macro ‘CPP2_UFCS_IDENTITY’
- 2047 |             return false;
+ 2047 |         )
       |                                  ^          
 ../../../include/cpp2util.h:2086:79: note: in expansion of macro ‘CPP2_FORWARD’
- 2086 | template<typename T, std::same_as<std::any> X>
+ 2086 | }
       |                                                                               ^           
 ../../../include/cpp2util.h:2107:22: note: in expansion of macro ‘CPP2_UFCS_CONSTRAINT_ARG’
- 2107 |     }
-      |                      ^                       
+ 2107 |     if constexpr (valid_predicate<decltype(value), decltype(x)>) {
+      |                      ^~~~~~~~~~~~~~~~~~~~~~~~
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 pure2-default-arguments.cpp2:6:22: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 ../../../include/cpp2util.h:2087:74: error: local variable ‘obj’ may not appear in this context
- 2087 | constexpr auto is( X const& x ) -> bool{
+ 2087 | 
       |                                                                          ^  
 ../../../include/cpp2util.h:2047:34: note: in definition of macro ‘CPP2_UFCS_IDENTITY’
- 2047 |             return false;
+ 2047 |         )
       |                                  ^          
 ../../../include/cpp2util.h:2087:61: note: in expansion of macro ‘CPP2_FORWARD’
- 2087 | constexpr auto is( X const& x ) -> bool{
+ 2087 | 
       |                                                             ^           
 ../../../include/cpp2util.h:2107:22: note: in expansion of macro ‘CPP2_UFCS_CONSTRAINT_ARG’
- 2107 |     }
-      |                      ^                       
+ 2107 |     if constexpr (valid_predicate<decltype(value), decltype(x)>) {
+      |                      ^~~~~~~~~~~~~~~~~~~~~~~~
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 pure2-default-arguments.cpp2:6:22: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 ../../../include/cpp2util.h:2087:93: error: local variable ‘params’ may not appear in this context
- 2087 | constexpr auto is( X const& x ) -> bool{
+ 2087 | 
       |                                                                                             ^     
 ../../../include/cpp2util.h:2047:34: note: in definition of macro ‘CPP2_UFCS_IDENTITY’
- 2047 |             return false;
+ 2047 |         )
       |                                  ^          
 ../../../include/cpp2util.h:2087:80: note: in expansion of macro ‘CPP2_FORWARD’
- 2087 | constexpr auto is( X const& x ) -> bool{
+ 2087 | 
       |                                                                                ^           
 ../../../include/cpp2util.h:2107:22: note: in expansion of macro ‘CPP2_UFCS_CONSTRAINT_ARG’
- 2107 |     }
-      |                      ^                       
+ 2107 |     if constexpr (valid_predicate<decltype(value), decltype(x)>) {
+      |                      ^~~~~~~~~~~~~~~~~~~~~~~~
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 pure2-default-arguments.cpp2:6:22: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 pure2-default-arguments.cpp2:6:61: error: ‘std::source_location’ has not been declared
diff --git a/regression-tests/test-results/gcc-14-c++2b/mixed-bugfix-for-ufcs-non-local.cpp.output b/regression-tests/test-results/gcc-14-c++2b/mixed-bugfix-for-ufcs-non-local.cpp.output
@@ -1,41 +1,41 @@
 In file included from mixed-bugfix-for-ufcs-non-local.cpp:6:
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 |         return value(x);
+ 2100 | }
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 mixed-bugfix-for-ufcs-non-local.cpp2:13:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:13:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 |         return value(x);
+ 2100 | }
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 mixed-bugfix-for-ufcs-non-local.cpp2:21:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:21:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 |         return value(x);
+ 2100 | }
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 mixed-bugfix-for-ufcs-non-local.cpp2:31:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:31:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 |         return value(x);
+ 2100 | }
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 mixed-bugfix-for-ufcs-non-local.cpp2:33:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:33:36: error: template argument 1 is invalid
 ../../../include/cpp2util.h:2100:1: error: lambda-expression in template parameter type
- 2100 |         return value(x);
+ 2100 | }
       | ^
 ../../../include/cpp2util.h:2137:59: note: in expansion of macro ‘CPP2_UFCS_’
- 2137 |     return false;
-      |                                                           ^         
+ 2137 | template<typename T, specialization_of_template<std::optional> X>
+      |                                                           ^~~~~~~   
 mixed-bugfix-for-ufcs-non-local.cpp2:21:12: note: in expansion of macro ‘CPP2_UFCS_NONLOCAL’
 mixed-bugfix-for-ufcs-non-local.cpp2:21:36: error: template argument 1 is invalid
diff --git a/regression-tests/test-results/gcc-14-c++2b/pure2-hashable.cpp.execution b/regression-tests/test-results/gcc-14-c++2b/pure2-hashable.cpp.execution
@@ -1 +1 @@
-6440649391998984779
+6443762454025613088
diff --git a/regression-tests/test-results/msvc-2022-c++latest/pure2-hashable.cpp.execution b/regression-tests/test-results/msvc-2022-c++latest/pure2-hashable.cpp.execution
@@ -1 +1 @@
-13958440649017415620
+13929407477532509065
diff --git a/regression-tests/test-results/pure2-hashable.cpp b/regression-tests/test-results/pure2-hashable.cpp
@@ -60,7 +60,7 @@ requires (std::is_convertible_v<CPP2_TYPEOF(h_), std::add_const_t<cpp2::i32>&>)
 [[nodiscard]] auto base::hash() const& -> size_t{
 
 size_t ret {0}; 
-ret ^= std::hash<cpp2::i32>()(h) + (ret << 6) + (ret >> 2);
+cpp2::hash_combine(ret, std::hash<cpp2::i32>()(h));
 return ret; 
 }
 
@@ -73,10 +73,10 @@ requires (std::is_convertible_v<CPP2_TYPEOF(i_), std::add_const_t<cpp2::i32>&> &
 [[nodiscard]] auto mystruct::hash() const& -> size_t{
 
 size_t ret {0}; 
-ret ^= base::hash() + (ret << 6) + (ret >> 2);
-ret ^= std::hash<cpp2::i32>()(i) + (ret << 6) + (ret >> 2);
-ret ^= std::hash<std::string>()(j) + (ret << 6) + (ret >> 2);
-ret ^= std::hash<cpp2::u64>()(k) + (ret << 6) + (ret >> 2);
+cpp2::hash_combine(ret, base::hash());
+cpp2::hash_combine(ret, std::hash<cpp2::i32>()(i));
+cpp2::hash_combine(ret, std::hash<std::string>()(j));
+cpp2::hash_combine(ret, std::hash<cpp2::u64>()(k));
 return ret; 
 }
 #line 12 "pure2-hashable.cpp2"

diff --git a/regression-tests/test-results/version b/regression-tests/test-results/version
@@ -1,5 +1,5 @@
 
-cppfront compiler v0.7.4   Build 9930:1349
+cppfront compiler v0.7.4   Build 9930:1408
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

diff --git a/source/build.info b/source/build.info
@@ -1 +1 @@
-"9930:1349"
+"9930:1408"
diff --git a/source/reflect.h b/source/reflect.h
@@ -2419,7 +2419,7 @@ auto hashable(meta::type_declaration& t) -> void
             o_hash.construct("std::hash<" + cpp2::to_string(CPP2_UFCS(type)(o)) + ">()(" + cpp2::to_string(CPP2_UFCS(name)(o)) + ")");
         }
 
-        hash += "\n        ret ^= " + cpp2::to_string(cpp2::move(o_hash.value())) + " + (ret << 6) + (ret >> 2);";
+        hash += "\n        cpp2::hash_combine( ret, " + cpp2::to_string(cpp2::move(o_hash.value())) + " );";
     }
 
     CPP2_UFCS(add_member)(t, cpp2::move(hash) + "\n        return ret;\n    }");

diff --git a/source/reflect.h2 b/source/reflect.h2
@@ -858,7 +858,7 @@ hashable: (inout t: meta::type_declaration) =
             o_hash = "std::hash<(o.type())$>()((o.name())$)";
         }
 
-        hash += "\n        ret ^= (o_hash)$ + (ret << 6) + (ret >> 2);";
+        hash += "\n        cpp2::hash_combine( ret, (o_hash)$ );";
     }
 
     t.add_member(hash + "\n        return ret;\n    }");