OrderedDict.move_to_end: alternate implementation of #8234

this implementation is hoped to be smaller. (feather_m4_express/fr fits
unlike the other PR; approximate savings ~600 bytes)

Minor difference to standard Python: A `dict` object has a
`move_to_end` method. However, calling this method always results in
TypeError.

Implementing it this way means that the method table can still be shared
between OrderedDict and builtin dict.

Closes #4408.

py/objdict.c

@@ -421,6 +421,53 @@ STATIC mp_obj_t dict_update(size_t n_args, const mp_obj_t *args, mp_map_t *kwarg
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(dict_update_obj, 1, dict_update);
 
+#if MICROPY_PY_COLLECTIONS_ORDEREDDICT
+STATIC mp_obj_t dict_move_to_end(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    mp_obj_dict_t *self = MP_OBJ_TO_PTR(pos_args[0]);
+    mp_arg_validate_type(self, &mp_type_ordereddict, MP_QSTR_self);
+
+    // parse args
+    enum { ARG_key, ARG_last };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_key, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE } },
+        { MP_QSTR_last, MP_ARG_BOOL, {.u_bool = true } }
+    };
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    mp_obj_t *key = args[ARG_key].u_obj;
+    bool last = args[ARG_last].u_bool;
+
+    mp_map_elem_t *elem = mp_map_lookup(&self->map, key, MP_MAP_LOOKUP);
+    if (!elem) {
+        mp_raise_type_arg(&mp_type_KeyError, key);
+    }
+
+    mp_map_elem_t tmp = *elem;
+    mp_map_elem_t *table = self->map.table;
+    mp_map_elem_t *dest, *move_begin, *move_dest;
+    size_t move_count;
+
+    if (last) {
+        mp_map_elem_t *top = &table[self->map.used];
+        dest = top - 1;
+        move_begin = elem + 1;
+        move_dest = elem;
+        move_count = top - move_begin;
+    } else {
+        dest = &table[0];
+        move_begin = table;
+        move_dest = table + 1;
+        move_count = elem - table;
+    }
+    memmove(move_dest, move_begin, move_count * sizeof(*elem));
+    *dest = tmp;
+
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_KW(dict_move_to_end_obj, 1, dict_move_to_end);
+#endif
+
 
 /******************************************************************************/
 /* dict views                                                                 */
@@ -590,6 +637,9 @@ STATIC const mp_rom_map_elem_t dict_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_get), MP_ROM_PTR(&dict_get_obj) },
     { MP_ROM_QSTR(MP_QSTR_items), MP_ROM_PTR(&dict_items_obj) },
     { MP_ROM_QSTR(MP_QSTR_keys), MP_ROM_PTR(&dict_keys_obj) },
+    #if MICROPY_PY_COLLECTIONS_ORDEREDDICT
+    { MP_ROM_QSTR(MP_QSTR_move_to_end), MP_ROM_PTR(&dict_move_to_end_obj) },
+    #endif
     { MP_ROM_QSTR(MP_QSTR_pop), MP_ROM_PTR(&dict_pop_obj) },
     { MP_ROM_QSTR(MP_QSTR_popitem), MP_ROM_PTR(&dict_popitem_obj) },
     { MP_ROM_QSTR(MP_QSTR_setdefault), MP_ROM_PTR(&dict_setdefault_obj) },

tests/basics/ordereddict2.py

@@ -0,0 +1,44 @@
+try:
+    from collections import OrderedDict
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+try:
+    {'a': None}.move_to_end('a')
+except (TypeError, AttributeError):
+    print("Exception")
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('a')
+print(list(d.items()))
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('b')
+print(list(d.items()))
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('c')
+print(list(d.items()))
+
+try:
+    d.move_to_end('x')
+except KeyError:
+    print("KeyError")
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('a', last=False)
+print(list(d.items()))
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('b', last=False)
+print(list(d.items()))
+
+d = OrderedDict(a=1, b=2, c=3)
+d.move_to_end('c', last=False)
+print(list(d.items()))
+
+try:
+    d.move_to_end('x', last=False)
+except KeyError:
+    print("KeyError")