Add macro M_CONST_CAST

m-core.h

@@ -593,6 +593,17 @@
 # define M_ASSIGN_CAST(type, n)                 static_cast<type>(n)
 #endif
 
+/* Cast 'n' of type 'type*' into 'const type*'.
+   This is like (const type*)p but safer as the type of 'n' is checked,
+   and more robust for double arrays type.
+*/
+#ifndef __cplusplus
+# define M_CONST_CAST(type, n)                          \
+  (((union { type *ptr; const type *cptr; }){n}).cptr)
+#else
+# define M_CONST_CAST(type, n)                  const_cast<const type*>(n)
+#endif
+
 /*
  * From a pointer to a 'field_type' 'field' of a 'type'structure,
  * return pointer to the structure.

tests/test-mcore.c

@@ -208,6 +208,17 @@ static void test_oplist(void)
   assert (!CHECK_OPLIST (CLEAR_TOOT, M_DEFAULT_OPLIST));
 }
 
+static void test_cast(void)
+{
+  float f1 = 1.0;
+  float f2 = M_ASSIGN_CAST(float, f1);
+  int   i1 = M_ASSIGN_CAST(int, f2);
+  assert (i1 == 1);
+  int *p1 = &i1;
+  const int *p2 = M_CONST_CAST(int, p1);
+  assert (*p2 == 1);
+}
+
 int main(void)
 {
   test_cat();
@@ -222,5 +233,6 @@ int main(void)
   test_va();
   test_if();
   test_oplist();
+  test_cast();
   exit(0);
 }