Merge pull request #329 from cppalliance/hash

Add support for std::hash to decimal128

include/boost/decimal/detail/emulated128.hpp

@@ -135,7 +135,7 @@ struct uint128
     constexpr auto operator=(const boost::uint128_type& v) noexcept -> uint128& { *this = uint128(v); return *this; }
     #endif
 
-    constexpr auto operator=(const uint128&) noexcept -> uint128&;
+    constexpr uint128& operator=(const uint128&) noexcept = default;
 
     #undef SIGNED_ASSIGNMENT_OPERATOR
     #undef UNSIGNED_ASSIGNMENT_OPERATOR
@@ -653,13 +653,6 @@ constexpr auto operator+(uint128 val) noexcept -> uint128
     return val;
 }
 
-constexpr auto uint128::operator=(const uint128& v) noexcept -> uint128&
-{
-    low = v.low;
-    high = v.high;
-    return *this;
-}
-
 constexpr auto operator==(uint128 lhs, uint128 rhs) noexcept -> bool
 {
     return lhs.high == rhs.high && lhs.low == rhs.low;

include/boost/decimal/hash.hpp

@@ -7,6 +7,7 @@
 
 #include <boost/decimal/decimal32.hpp>
 #include <boost/decimal/decimal64.hpp>
+#include <boost/decimal/decimal128.hpp>
 #include <functional>
 #include <cstring>
 
@@ -38,6 +39,28 @@ struct hash<boost::decimal::decimal64>
     }
 };
 
+#if __GNUC__ >= 8
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wclass-memaccess"
+#endif
+
+template <>
+struct hash<boost::decimal::decimal128>
+{
+    // Take the xor of the two words and hash that
+    auto operator()(const boost::decimal::decimal128& v) const noexcept -> std::size_t
+    {
+        boost::decimal::detail::uint128 bits;
+        std::memcpy(&bits, &v, sizeof(boost::decimal::detail::uint128));
+
+        return std::hash<std::uint64_t>{}(bits.high ^ bits.low);
+    }
+};
+
+#if __GNUC__ >= 8
+#  pragma GCC diagnostic pop
+#endif
+
 }
 
 #endif //BOOST_DECIMAL_HASH_HPP

test/Jamfile

@@ -51,6 +51,7 @@ run test_fenv.cpp ;
 run test_float_conversion.cpp ;
 run test_frexp_ldexp.cpp ;
 run test_git_issue_271.cpp ;
+run test_hash.cpp ;
 run test_literals.cpp ;
 run test_log.cpp ;
 run test_log1p.cpp ;

test/test_hash.cpp

@@ -0,0 +1,29 @@
+// Copyright 2023 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// This is a toy example to make sure that the hashing compiles correctly
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <functional>
+
+template <typename T>
+void test_hash()
+{
+    std::hash<T> hasher;
+    for (int i = 0; i < 100; ++i)
+    {
+        T dec_val(i);
+        BOOST_TEST_EQ(hasher(dec_val), hasher(dec_val));
+    }
+}
+
+int main()
+{
+    test_hash<boost::decimal::decimal32>();
+    test_hash<boost::decimal::decimal64>();
+    test_hash<boost::decimal::decimal128>();
+
+    return boost::report_errors();
+}