From 0485b0128a3932a1d0ea5b0bac30105072a84aa9 Mon Sep 17 00:00:00 2001
From: Grant McDermott <gmcd@amazon.com>
Date: Sun, 26 Oct 2025 17:13:26 -0700
Subject: [PATCH 1/2] add configure script for OpenMP support

- adapted from data.table
---
 configure       | 58 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/Makevars.in |  4 ++++
 2 files changed, 62 insertions(+)
 create mode 100755 configure
 create mode 100644 src/Makevars.in

diff --git a/configure b/configure
new file mode 100755
index 00000000..587aff85
--- /dev/null
+++ b/configure
@@ -0,0 +1,58 @@
+#!/usr/bin/env sh
+
+# Find R compilers
+CC=`${R_HOME}/bin/R CMD config CC`
+CFLAGS=`${R_HOME}/bin/R CMD config CFLAGS`
+CXX=`${R_HOME}/bin/R CMD config CXX`
+CXXFLAGS=`${R_HOME}/bin/R CMD config CXXFLAGS`
+
+# Test if we have OpenMP support
+cat <<EOF > test-omp.cpp
+#include <omp.h>
+int main() {
+  return omp_get_num_threads();
+}
+EOF
+
+detect_openmp () {
+  if [ "$(uname)" = "Darwin" ]; then
+    # Test for macOS OpenMP support
+    printf "%s" "* checking if R installation supports OpenMP with \"-Xclang -fopenmp\" ... "
+    if CPPFLAGS="${CPPFLAGS} -Xclang -fopenmp" PKG_LIBS="-lomp" "${R_HOME}/bin/R" CMD SHLIB test-omp.cpp >> config.log 2>&1; then
+      echo "yes"
+      export R_OPENMP_ENABLED=1
+      return
+    else
+      echo "no"
+    fi
+  fi
+
+  if [ "$(uname)" = "Linux" ]; then
+    # Test for Linux OpenMP support
+    printf "%s" "* checking if R installation supports OpenMP with \"-fopenmp\" ... "
+    if ${CXX} ${CXXFLAGS} -fopenmp test-omp.cpp >> config.log 2>&1; then
+      echo "yes"
+      export R_OPENMP_ENABLED=1
+      return
+    else
+      echo "no"
+    fi
+  fi
+
+  # No OpenMP support found
+  export R_OPENMP_ENABLED=0
+}
+
+detect_openmp
+rm -f test-omp.* a.out
+
+# Generate Makevars from template based on OpenMP detection
+if [ "${R_OPENMP_ENABLED}" = "0" ]; then
+  echo "*** OpenMP not supported! fixest will run single-threaded."
+  sed -e "s/\$(SHLIB_OPENMP_CXXFLAGS)//g" src/Makevars.in > src/Makevars
+else
+  # Keep the template as-is (OpenMP variables will be expanded by R)
+  cp src/Makevars.in src/Makevars
+fi
+
+exit 0
diff --git a/src/Makevars.in b/src/Makevars.in
new file mode 100644
index 00000000..4fc90886
--- /dev/null
+++ b/src/Makevars.in
@@ -0,0 +1,4 @@
+
+PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS) -DSTRICT_R_HEADERS
+PKG_LIBS = $(SHLIB_OPENMP_CXXFLAGS)
+

From 22aa2e989f6bf60f38caef473d5d906354962db7 Mon Sep 17 00:00:00 2001
From: Grant McDermott <gmcd@amazon.com>
Date: Sun, 26 Oct 2025 17:13:46 -0700
Subject: [PATCH 2/2] ignore config build log

---
 .gitignore | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.gitignore b/.gitignore
index 65318205..81896181 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,3 +20,7 @@ altdoc/freeze.rds
 _quarto/*
 !_quarto/_freeze/
 .DS_Store
+
+# Configure script outputs
+config.log
+src/Makevars