std::hash example

Author: davidbrowne

VS2022/dsga.vcxproj

@@ -176,6 +176,7 @@
     <ClInclude Include="..\examples\basic.hxx" />
     <ClInclude Include="..\examples\bezier.hxx" />
     <ClInclude Include="..\examples\format_output.hxx" />
+    <ClInclude Include="..\examples\hash.hxx" />
     <ClInclude Include="..\examples\ostream_output.hxx" />
     <ClInclude Include="..\examples\span_convert.hxx" />
     <ClInclude Include="..\examples\stl.hxx" />

VS2022/dsga.vcxproj.filters

@@ -45,6 +45,9 @@
     <ClInclude Include="..\examples\basic.hxx">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\examples\hash.hxx">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <None Include="..\README.md" />

examples/hash.hxx

@@ -0,0 +1,56 @@
+
+//          Copyright David Browne 2020-2023.
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          https://www.boost.org/LICENSE_1_0.txt)
+
+#include "dsga.hxx"
+#include <functional>
+
+
+// based on https://www.boost.org/doc/libs/1_83_0/libs/container_hash/doc/html/hash.html#notes_hash_combine
+template <typename T>
+constexpr std::size_t hash_combine(std::size_t seed, const T &t) noexcept
+{
+	std::size_t x = seed + 0x9e3779b9 + std::hash<T>{}(t);
+
+	x ^= x >> 32;
+	x *= 0xe9846af9b1a615d;
+	x ^= x >> 32;
+	x *= 0xe9846af9b1a615d;
+	x ^= x >> 28;
+
+	return x;
+}
+
+template <dsga::dimensional_scalar T, std::size_t S>
+struct std::hash<dsga::basic_vector<T, S>>
+{
+	std::size_t operator()(const dsga::basic_vector<T, S> &v) const noexcept
+	{
+		std::size_t seed = 0;
+
+		[&] <std::size_t ...Js>(std::index_sequence<Js ...>)
+		{
+			((seed = hash_combine(seed, v[Js])), ...);
+		}(std::make_index_sequence<S>{});
+
+		return seed;
+	}
+};
+
+template <dsga::floating_point_scalar T, std::size_t C, std::size_t R>
+struct std::hash<dsga::basic_matrix<T, C, R>>
+{
+	std::size_t operator()(const dsga::basic_matrix<T, C, R> &m) const noexcept
+	{
+		std::size_t seed = 0;
+
+		[&] <std::size_t ...Js>(std::index_sequence<Js ...>)
+		{
+			((seed = hash_combine(seed, m[Js])), ...);
+		}(std::make_index_sequence<C>{});
+
+		return seed;
+	}
+};