replace CL_REQUIRE/CL_PROVIDE(cl_0_ring) with (more) portable code.

The order of initialization of non-local objects in different compilation units
is not specified in C++. Hence special care should be taken to avoid static
initialization order fiasco. CLN solved the problem with some evil (GCC
specific, and even GCC-version-specific) hack. Replace it with a technique
similar to one used in STL to initialize std::cout and friends.

include/cln/null_ring.h

@@ -9,7 +9,15 @@ namespace cln {
 
 class cl_null_ring : public cl_ring { public: cl_null_ring (); };
 extern const cl_null_ring cl_0_ring;		// math. {0}
-//CL_REQUIRE(cl_0_ring)
+
+class cl_0_ring_init_helper
+{
+	static int count;
+public:
+	cl_0_ring_init_helper();
+	~cl_0_ring_init_helper();
+};
+static cl_0_ring_init_helper cl_0_ring_init_helper_instance;
 
 }  // namespace cln
 

src/integer/ring/cl_0_ring.cc

@@ -3,7 +3,6 @@
 // General includes.
 #include "cl_sysdep.h"
 
-CL_PROVIDE(cl_0_ring)
 
 // Specification.
 #include "cln/null_ring.h"
@@ -74,34 +73,48 @@ static const _cl_ring_element null_expt_pos (cl_heap_ring* R, const _cl_ring_ele
 	return _cl_ring_element(R, (cl_I)0);
 }
 
-static cl_ring_setops null_setops = {
-	null_fprint,
-	null_equal
-};
-static cl_ring_addops null_addops = {
-	null_zero,
-	null_zerop,
-	null_plus,
-	null_minus,
-	null_uminus
-};
-static cl_ring_mulops null_mulops = {
-	null_one,
-	null_canonhom,
-	null_mul,
-	null_square,
-	null_expt_pos
-};
+static cl_ring_setops& null_setops()
+{
+	static cl_ring_setops ops = {
+		null_fprint,
+		null_equal
+	};
+	return ops;
+}
+
+static cl_ring_addops& null_addops()
+{
+	static cl_ring_addops ops = {
+		null_zero,
+		null_zerop,
+		null_plus,
+		null_minus,
+		null_uminus
+	};
+	return ops;
+}
+
+static cl_ring_mulops& null_mulops()
+{
+	static cl_ring_mulops ops = {
+		 null_one,
+		 null_canonhom,
+		 null_mul,
+		 null_square,
+		 null_expt_pos
+	};
+	return ops;
+}
 
-extern cl_class cl_class_null_ring;
+static const cl_class& cl_class_null_ring();
 
 class cl_heap_null_ring : public cl_heap_ring {
 	SUBCLASS_cl_heap_ring()
 public:
 	// Constructor.
 	cl_heap_null_ring ()
-		: cl_heap_ring (&null_setops,&null_addops,&null_mulops)
-		{ type = &cl_class_null_ring; }
+		: cl_heap_ring (&null_setops(),&null_addops(),&null_mulops())
+		{ type = &cl_class_null_ring(); }
 	// Destructor.
 	~cl_heap_null_ring () {}
 };
@@ -117,17 +130,38 @@ static void cl_null_ring_dprint (cl_heap* pointer)
 	fprint(cl_debugout, "(cl_null_ring) cl_0_ring");
 }
 
-cl_class cl_class_null_ring = {
-	cl_null_ring_destructor,
-	cl_class_flags_number_ring,
-	cl_null_ring_dprint
-};
+static const cl_class& cl_class_null_ring()
+{
+	static const cl_class cl_class_null_ring_instance = {
+		 cl_null_ring_destructor,
+		 cl_class_flags_number_ring,
+		 cl_null_ring_dprint
+	};
+	return cl_class_null_ring_instance;
+}
+
+cl_heap_null_ring* cl_heap_null_ring_instance;
+const cl_null_ring cl_0_ring = cl_0_ring;
 
 inline cl_null_ring::cl_null_ring ()
-	: cl_ring (new cl_heap_null_ring()) {}
+	: cl_ring(cl_heap_null_ring_instance) {}
+
+int cl_0_ring_init_helper::count = 0;
 
-const cl_null_ring cl_0_ring;
+cl_0_ring_init_helper::cl_0_ring_init_helper()
+{
+	if (count++ == 0) {
+		cl_heap_null_ring_instance = new cl_heap_null_ring();
+		new ((void *)&cl_0_ring) cl_null_ring();
+	 }
+}
+
+cl_0_ring_init_helper::~cl_0_ring_init_helper()
+{
+	if (--count == 0) {
+		 delete cl_heap_null_ring_instance;
+	}
+}
 
 }  // namespace cln
 
-CL_PROVIDE_END(cl_0_ring)