diff -r 38fa7e41194c -r 53e22f112b11 configure
--- a/configure	Mon Nov 11 21:42:14 2024 +0100
+++ b/configure	Tue Nov 12 17:34:04 2024 +0100
@@ -113,6 +113,7 @@
 
 Optional Features:
   --enable-coverage
+  --disable-szmul-builtin use custom implementation, instead
 
 __EOF__
 }
@@ -158,6 +159,7 @@
 fi
 
 # features
+FEATURE_SZMUL_BUILTIN=auto
 
 #
 # parse arguments
@@ -187,6 +189,8 @@
         "--with-docs="*) OPT_WITH_DOCS=${ARG#--with-docs=} ;;
         "--enable-coverage") FEATURE_COVERAGE=on ;;
         "--disable-coverage") unset FEATURE_COVERAGE ;;
+        "--enable-szmul-builtin") FEATURE_SZMUL_BUILTIN=on ;;
+        "--disable-szmul-builtin") unset FEATURE_SZMUL_BUILTIN ;;
         "-"*) echo "unknown option: $ARG"; abort_configure ;;
     esac
 done
@@ -603,6 +607,23 @@
         unset FEATURE_COVERAGE
     fi
 fi
+if [ -n "$FEATURE_COVERAGE" ]; then
+    :
+else
+    :
+fi
+if [ -n "$FEATURE_SZMUL_BUILTIN" ]; then
+    if [ -n "$DISABLE_FEATURE_SZMUL_BUILTIN" ]; then
+        unset FEATURE_SZMUL_BUILTIN
+    fi
+fi
+if [ -n "$FEATURE_SZMUL_BUILTIN" ]; then
+    :
+else
+    :
+    TEMP_CFLAGS="$TEMP_CFLAGS -DCX_NO_SZMUL_BUILTIN"
+    TEMP_CXXFLAGS="$TEMP_CXXFLAGS -DCX_NO_SZMUL_BUILTIN"
+fi
 
 # Option: --with-docs
 if [ -z "$OPT_WITH_DOCS" ]; then
@@ -727,6 +748,11 @@
 else
 echo "  coverage: off"
 fi
+if [ -n "$FEATURE_SZMUL_BUILTIN" ]; then
+echo "  szmul-builtin: on"
+else
+echo "  szmul-builtin: off"
+fi
 echo
 
 # generate the config.mk file