From f0b282a69587453ae396ce0cfd1f140310cc1e38 Mon Sep 17 00:00:00 2001
From: Richard E Barber <kd6kxr@gmail.com>
Date: Mon, 28 Aug 2023 09:32:43 -0700
Subject: [PATCH] Create findATOMIC.cmake

Provided by @Floessie  https://github.com/Beep6581/RawTherapee/issues/6821#issuecomment-1678626624
---
 cmake/modules/findATOMIC.cmake | 36 ++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 cmake/modules/findATOMIC.cmake

diff --git a/cmake/modules/findATOMIC.cmake b/cmake/modules/findATOMIC.cmake
new file mode 100644
index 000000000..1669983c3
--- /dev/null
+++ b/cmake/modules/findATOMIC.cmake
@@ -0,0 +1,36 @@
+include(CheckCXXSourceCompiles)
+
+set(ATOMIC_CXX_TEST_SOURCE
+"
+#include <atomic>
+int main() {
+	std::atomic<bool> b(false);
+	std::atomic<int> i(0);
+	std::atomic<unsigned int> ui(0);
+	b.exchange(true);
+	++i;
+	return ++ui;
+}
+")
+
+set(SAFE_CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES}")
+list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES "atomic")
+
+check_cxx_source_compiles("${ATOMIC_CXX_TEST_SOURCE}" HAVE_CXX_ATOMICS_WITHOUT_LIB)
+
+if(NOT HAVE_CXX_ATOMICS_WITHOUT_LIB)
+	list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+	check_cxx_source_compiles("${ATOMIC_CXX_TEST_SOURCE}" HAVE_CXX_ATOMICS_WITH_LIB)
+	if (NOT HAVE_CXX_ATOMICS_WITH_LIB)
+		message(FATAL_ERROR "libatomic support needed for std::atomic<> but not 
+found.")
+	endif()
+	set(ATOMIC_LIBRARIES "atomic")
+	set(ATOMIC_FOUND ON)
+endif()
+
+set(CMAKE_REQUIRED_LIBRARIES "${SAFE_CMAKE_REQUIRED_LIBRARIES}")
+unset(SAFE_CMAKE_REQUIRED_LIBRARIES)
+
+mark_as_advanced(ATOMIC_LIBRARIES)
+mark_as_advanced(ATOMIC_FOUND)