From 5ab6d2853877b4c917343dc35a4a5e3009b60289 Mon Sep 17 00:00:00 2001
From: Paul Ramsey <pramsey@cleverelephant.ca>
Date: Wed, 10 Jan 2024 14:06:45 -0800
Subject: [PATCH] Fix regression tests for AppleClang on ARM64

---
 CMakeLists.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cd210afb23..bf9590f65f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -154,6 +154,20 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 add_library(geos_cxx_flags INTERFACE)
 target_compile_features(geos_cxx_flags INTERFACE cxx_std_11)
 
+#-----------------------------------------------------------------------------
+# Add flags to prevent 'fused multiply-add' operations on targets (ARM64)
+# that allow it, as it breaks calculations in DD.cpp.
+# TODO: Replace DD calculations with 'long float' where target supports
+# true long float, and remove other cases where FMA causes regression
+# failures.
+#   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98207
+#-----------------------------------------------------------------------------
+target_compile_options(geos_cxx_flags INTERFACE
+	"$<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:-ffp-contract=off>"
+	"$<$<CXX_COMPILER_ID:GNU>:-ffp-contract=off>"
+	"$<$<CXX_COMPILER_ID:MSVC>:/fp:precise>"
+	)
+
 #-----------------------------------------------------------------------------
 # Target geos_cxx_flags: common compilation flags
 #-----------------------------------------------------------------------------