Introduce AtomIndex type

Signed-off-by: Paul Guyot <pguyot@kallisys.net>

Author: pguyot

src/libAtomVM/atom.h

@@ -45,6 +45,7 @@ extern "C" {
 #define ATOM_STR(LENSTR, STR) (LENSTR STR)
 
 typedef const void *AtomString;
+typedef uint32_t AtomIndex;
 
 /**
  * @brief Gets a C string from an AtomString

src/libAtomVM/term.h

@@ -37,6 +37,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "atom.h"
 #include "memory.h"
 #include "refc_binary.h"
 #include "utils.h"
@@ -599,7 +600,7 @@ static inline term term_nil()
  * @param t the term that will be converted to atom table index. t must be a valid atom term.
  * @return a global atom table index.
  */
-static inline int term_to_atom_index(term t)
+static inline AtomIndex term_to_atom_index(term t)
 {
     return t >> 6;
 }
@@ -611,7 +612,7 @@ static inline int term_to_atom_index(term t)
  * @param atom_index global atoms table index.
  * @return a term that encapsulates the atom.
  */
-static inline term term_from_atom_index(int atom_index)
+static inline term term_from_atom_index(AtomIndex atom_index)
 {
     return TERM_FROM_ATOM_INDEX(atom_index);
 }