Use std::signed_integral concept

...which, unlike std::is_signed, also requires that T is an integer type, not
just any arithmetic type, but which appears to fit well here anyway.

But LLVM 12 libc++, which is apparently used by Android builds, only provides a
bare-bones <concepts> that lacks std::signed_integral (among others), so for now
introduce o3tl/concepts.hxx providing what's missing (incl. std::integral and
std::unsigned_integral, for some kind of consistency).

Change-Id: I1c37d37fa1b57b5e3bf24c9e44f3973003905cb2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/158406
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/include/o3tl/concepts.hxx b/include/o3tl/concepts.hxx
new file mode 100644
index 000000000000..261d063ebca2
--- /dev/null
+++ b/include/o3tl/concepts.hxx
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * 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
+
+#include <sal/config.h>
+
+#include <concepts>
+
+// LLVM 12 libc++ only provides a bare-bones <concepts> that lacks most of its C++20 content, so
+// replicate here fore now what we need:
+
+#if defined __cpp_lib_concepts
+
+namespace o3tl
+{
+using std::integral;
+using std::signed_integral;
+using std::unsigned_integral;
+}
+
+#else
+
+#include <type_traits>
+
+namespace o3tl
+{
+// Taken from the C++20 spec:
+
+template <typename T> concept integral = std::is_integral_v<T>;
+
+template <typename T> concept signed_integral = integral<T>&& std::is_signed_v<T>;
+
+template <typename T> concept unsigned_integral = integral<T> && !signed_integral<T>;
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */