always use the pure C++ code implementation of uint320 for msvc

makefile

@@ -1,4 +1,4 @@
-CC := g++
+CXX := g++
 TESTFLAGS := -g -Og -D_HIDE_WARNING
 CXXFLAGS := -std=c++11 -Wall -Wextra
 
@@ -62,9 +62,9 @@ header_test: $(OBJ)
 # -------------------------- test program compilation ---------------------------
 
 $(SRC)/%.out: $(SRC)/%.cpp
-# @echo "compiling test program - compiler : $(CC)"
+# @echo "compiling test program - compiler : $(CXX)"
 # @echo "flags: $<"
-	$(CC) $(TESTFLAGS) $(CXXFLAGS) -o $@ $<
+	$(CXX) $(TESTFLAGS) $(CXXFLAGS) -o $@ $<
 
 clean:
 ifeq ($(OS), Linux)

uint320.cpp

@@ -111,6 +111,12 @@ bool uint320::operator>=(const uint320& with) const {
 uint320& uint320::operator+=(const uint320& add) {
 
 #if(__x86_64 || __x86_64__ || __amd64 || __amd64__ || __aarch64__ || _WIN64)
+
+#if(_MSC_VER)
+// assign 1 here since msvc does not accept just definition unlike clang and gcc
+#define _PURE_CPP 1
+#endif
+
 #if(_MSC_VER || _PURE_CPP)
     __uint128_t sum_uint128[UINT320LIMBS+1] = {0,0,0,0,0,0};