add o3tl version of hash_combine to not depend on boost for this

Change-Id: I081f8d116ef811baa8aa5de35a6cb51fa4de7d56
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/114983
Tested-by: Tomaž Vajngerl <quikee@gmail.com>
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/include/o3tl/hash_combine.hxx b/include/o3tl/hash_combine.hxx
new file mode 100644
index 000000000000..17419b3e2c0f
--- /dev/null
+++ b/include/o3tl/hash_combine.hxx
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#pragma once
+
+namespace o3tl
+{
+template <typename T, typename N, std::enable_if_t<(sizeof(N) == 4), bool> = false>
+inline void hash_combine(N& nSeed, T const& nValue)
+{
+    static_assert(sizeof(nSeed) == 4);
+    nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B9u + (nSeed << 6) + (nSeed >> 2);
+}
+
+template <typename T, typename N, std::enable_if_t<(sizeof(N) == 8), bool> = false>
+inline void hash_combine(N& nSeed, T const& nValue)
+{
+    static_assert(sizeof(nSeed) == 8);
+    nSeed ^= std::hash<T>{}(nValue) + 0x9E3779B97F4A7C15llu + (nSeed << 12) + (nSeed >> 4);
+}
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */