py: Make id() return small int for the most common address space mapping.

Many OSes/CPUs have affinity to put "user" data into lower half of address
space. Take advantage of that and remap such addresses into full small int
range (including negative part).

If address is from upper half, long int will be used. Previously, small
int was returned for lower quarter of address space, and upper quarter. For
2 middle quarters, long int was used, which is clearly worse schedule than
the above.

py/builtin.c

@@ -503,7 +503,21 @@ STATIC mp_obj_t mp_builtin_sorted(uint n_args, const mp_obj_t *args, mp_map_t *k
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj, 1, mp_builtin_sorted);
 
 STATIC mp_obj_t mp_builtin_id(mp_obj_t o_in) {
-    return mp_obj_new_int((mp_int_t)o_in);
+    mp_int_t id = (mp_int_t)o_in;
+    if (!MP_OBJ_IS_OBJ(o_in)) {
+        return mp_obj_new_int(id);
+    } else if (id >= 0) {
+        // Many OSes and CPUs have affinity for putting "user" memories
+        // into low half of address space, and "system" into upper half.
+        // We're going to take advantage of that and return small int
+        // (signed) for such "user" addresses.
+        return MP_OBJ_NEW_SMALL_INT(id);
+    } else {
+        // If that didn't work, well, let's return long int, just as
+        // a (big) positve value, so it will never clash with the range
+        // of small int returned in previous case.
+        return mp_obj_new_int_from_uint((mp_uint_t)id);
+    }
 }
 
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_id_obj, mp_builtin_id);