From 10d2daf54484fcfff8f8749a5792acd7f16f96f7 Mon Sep 17 00:00:00 2001
From: Thomas Debesse <dev@illwieckz.net>
Date: Wed, 22 Mar 2023 07:03:57 +0100
Subject: [PATCH] cmake: add USE_FLOAT_EXCEPTIONS to enable floating point
 exceptions

---
 cmake/DaemonFlags.cmake         | 20 +++++++-
 src/engine/framework/System.cpp | 87 +++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+), 2 deletions(-)

diff --git a/cmake/DaemonFlags.cmake b/cmake/DaemonFlags.cmake
index 5b069e1e76..94f1f32ebf 100644
--- a/cmake/DaemonFlags.cmake
+++ b/cmake/DaemonFlags.cmake
@@ -148,13 +148,20 @@ else()
     set(WARNMODE "no-")
 endif()
 
+# Compiler options
+option(USE_FLOAT_EXCEPTIONS "Use floating point exceptions" OFF)
 option(USE_FAST_MATH "Use fast math" ON)
 
-# Compiler options
+if (USE_FLOAT_EXCEPTIONS)
+	add_definitions(-DDAEMON_USE_FLOAT_EXCEPTIONS)
+endif()
+
 if (MSVC)
     set_c_cxx_flag("/MP")
 
-	if (USE_FAST_MATH)
+	if (USE_FLOAT_EXCEPTIONS)
+		set_c_cxx_flag("/fp:strict")
+	elseif (USE_FAST_MATH)
 		set_c_cxx_flag("/fp:fast")
 	endif()
 
@@ -248,6 +255,15 @@ else()
 		set_c_cxx_flag("-ffast-math")
 	endif()
 
+	if (USE_FLOAT_EXCEPTIONS)
+		# Floating point exceptions requires trapping math
+		# to avoid false positives on architectures with SSE.
+		set_c_cxx_flag("-ftrapping-math")
+		# GCC prints noisy warnings saying -ftrapping-math implies this.
+		set_c_cxx_flag("-fno-associative-math")
+		# Other optimizations from -ffast-math can be kept.
+	endif()
+
 	# Use hidden symbol visibility if possible.
 	try_c_cxx_flag(FVISIBILITY_HIDDEN "-fvisibility=hidden")
 
diff --git a/src/engine/framework/System.cpp b/src/engine/framework/System.cpp
index 593b94e207..b3b6e47230 100644
--- a/src/engine/framework/System.cpp
+++ b/src/engine/framework/System.cpp
@@ -51,6 +51,28 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sys/file.h>
 #endif
 
+#if defined(DAEMON_USE_FLOAT_EXCEPTIONS)
+	#if defined(__USE_GNU) || defined (__APPLE__)
+		#include <cfenv>
+		#define DAEMON_USE_FLOAT_EXCEPTIONS_AVAILABLE
+	#elif defined(_MSC_VER)
+		#include <cfloat>
+		#define DAEMON_USE_FLOAT_EXCEPTIONS_AVAILABLE
+	#endif
+#endif
+
+#if defined(DAEMON_USE_FLOAT_EXCEPTIONS_AVAILABLE)
+	static Cvar::Cvar<bool> common_floatExceptions_invalid("common.floatExceptions.invalid",
+		"enable floating point exception for operation with NaN",
+		Cvar::INIT, false);
+	static Cvar::Cvar<bool> common_floatExceptions_divByZero("common.floatExceptions.divByZero",
+		"enable floating point exception for division-by-zero operation",
+		Cvar::INIT, false);
+	static Cvar::Cvar<bool> common_floatExceptions_overflow("common.floatExceptions.overflow",
+		"enable floating point exception for operation producing an overflow",
+		Cvar::INIT, false);
+#endif
+
 namespace Sys {
 static Cvar::Cvar<bool> cvar_common_shutdownOnDrop("common.shutdownOnDrop", "shut down engine on game drop", Cvar::TEMPORARY, false);
 
@@ -276,6 +298,69 @@ static void CloseSingletonSocket()
 #endif
 }
 
+static void SetFloatingPointExceptions()
+{
+	// Must be done after Sys::Init() to read cvars from command line.
+	#if defined(DAEMON_USE_FLOAT_EXCEPTIONS_AVAILABLE)
+		#if defined(__USE_GNU) || defined(__APPLE__)
+			int exceptions = 0;
+		#elif defined(_MSC_VER)
+			unsigned int exceptions = 0;
+		#endif
+
+		// Operations with NaN.
+		if (common_floatExceptions_invalid.Get())
+		{
+			#if defined(__USE_GNU)
+				exceptions |= FE_INVALID;
+			#elif defined(__APPLE__)
+				exceptions |= __fpcr_trap_invalid;
+			#elif defined(_MSC_VER)
+				exceptions |= _EM_INVALID
+			#endif
+		}
+
+		// Division by zero.
+		if (common_floatExceptions_divByZero.Get())
+		{
+			#if defined(__USE_GNU)
+				exceptions |= FE_DIVBYZERO;
+			#elif defined(__APPLE__)
+				exceptions |= __fpcr_trap_divbyzero;
+			#elif defined(_MSC_VER)
+				exceptions |= _EM_ZERODIVIDE;
+			#endif
+		}
+
+		// Operations producing an overflow.
+		if (common_floatExceptions_overflow.Get())
+		{
+			#if defined(__USE_GNU)
+				exceptions |= FE_OVERFLOW;
+			#elif defined(__APPLE__)
+				exceptions |= __fpcr_trap_overflow;
+			#elif defined(_MSC_VER)
+				exceptions |= _EM_OVERFLOW;
+			#endif
+		}
+
+		#if defined(__USE_GNU)
+			// https://www.gnu.org/savannah-checkouts/gnu/libc/manual/html_node/Control-Functions.html
+			feenableexcept(exceptions);
+		#elif defined(__APPLE__)
+			// https://stackoverflow.com/a/71792418
+			fenv_t env;
+			fegetenv(&env);
+			env.__fpcr = env.__fpcr | exceptions;
+		    fesetenv(&env);
+		#elif defined(_MSC_VER)
+			// https://learn.microsoft.com/en-us/previous-versions/visualstudio/visual-studio-2012/c9676k6h(v=vs.110)
+			unsigned int current;
+			_controlfp_s(&current, exceptions, _MCW_EM);
+		#endif
+	#endif
+}
+
 // Common code for fatal and non-fatal exit
 // TODO: Handle shutdown requests coming from multiple threads (could happen from the *nix signal thread)
 static void Shutdown(bool error, Str::StringRef message)
@@ -656,6 +741,8 @@ static void Init(int argc, char** argv)
 	// Set cvars set from the command line having the Cvar::INIT flag
 	SetCvarsWithInitFlag(cmdlineArgs);
 
+	SetFloatingPointExceptions();
+
 	// Initialize the filesystem. For pakpaths, the libpath is added first and has the
 	// lowest priority, while the homepath is added last and has the highest.
 	cmdlineArgs.pakPaths.insert(cmdlineArgs.pakPaths.begin(), FS::Path::Build(cmdlineArgs.libPath, "pkg"));