py: Define and use MP_OBJ_ITER_BUF_NSLOTS to get size of stack iter buf.

It improves readability of code and reduces the chance to make a mistake.

This patch also fixes a bug with nan-boxing builds by rounding up the
calculation of the new NSLOTS variable, giving the correct number of slots
(being 4) even if mp_obj_t is larger than the native machine size.

1 files changed, 4 insertions, 0 deletions

diff --git a/py/obj.h b/py/obj.h
index 93078b81e..fc122c490 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -422,6 +422,10 @@ typedef struct _mp_obj_iter_buf_t {
     mp_obj_t buf[3];
 } mp_obj_iter_buf_t;
 
+// The number of slots that an mp_obj_iter_buf_t needs on the Python value stack.
+// It's rounded up in case mp_obj_base_t is smaller than mp_obj_t (eg for OBJ_REPR_D).
+#define MP_OBJ_ITER_BUF_NSLOTS ((sizeof(mp_obj_iter_buf_t) + sizeof(mp_obj_t) - 1) / sizeof(mp_obj_t))
+
 typedef void (*mp_print_fun_t)(const mp_print_t *print, mp_obj_t o, mp_print_kind_t kind);
 typedef mp_obj_t (*mp_make_new_fun_t)(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args);
 typedef mp_obj_t (*mp_call_fun_t)(mp_obj_t fun, size_t n_args, size_t n_kw, const mp_obj_t *args);