Add std::hash overload

Author: mborland

include/boost/decimal/hash.hpp

@@ -65,6 +65,20 @@ struct hash<boost::decimal::decimal128>
 #  pragma GCC diagnostic pop
 #endif
 
+BOOST_DECIMAL_EXPORT template <>
+struct hash<boost::decimal::decimal32_fast>
+{
+    // Need to convert into decimal32 then apply our memcpy
+    auto operator()(const boost::decimal::decimal32_fast& v) const noexcept -> std::size_t
+    {
+        boost::decimal::decimal32 v_32 {v};
+        std::uint32_t bits;
+        std::memcpy(&bits, &v_32, sizeof(std::uint32_t));
+
+        return std::hash<std::uint32_t>{}(bits);
+    }
+};
+
 }
 
 #endif //BOOST_DECIMAL_HASH_HPP

test/test_decimal32_fast_basis.cpp

@@ -394,15 +394,13 @@ void spot_check_addition(T a, T b, T res)
     }
 }
 
-/*
 void test_hash()
 {
     decimal32_fast one {1, 0};
     decimal32_fast zero {0, 0};
 
     BOOST_TEST_NE(std::hash<decimal32_fast>{}(one), std::hash<decimal32_fast>{}(zero));
 }
- */
 
 void test_shrink_significand()
 {
@@ -439,7 +437,7 @@ int main()
     test_multiplicatiom();
     // test_div_mod();
 
-    // test_hash();
+    test_hash();
 
     spot_check_addition(-1054191000, -920209700, -1974400700);
     spot_check_addition(353582500, -32044770, 321537730);