py: Remove mp_obj_str_builder and use vstr instead.

With this patch str/bytes construction is streamlined.  Always use a
vstr to build a str/bytes object.  If the size is known beforehand then
use vstr_init_len to allocate only required memory.  Otherwise use
vstr_init and the vstr will grow as needed.  Then use
mp_obj_new_str_from_vstr to create a str/bytes object using the vstr
memory.

Saves code ROM: 68 bytes on stmhal, 108 bytes on bare-arm, and 336 bytes
on unix x64.

1 files changed, 4 insertions, 3 deletions

diff --git a/py/objint.c b/py/objint.c
index 049d0410e..e8d86ad7e 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -340,8 +340,9 @@ STATIC mp_obj_t int_to_bytes(mp_uint_t n_args, const mp_obj_t *args) {
     mp_int_t val = mp_obj_int_get_checked(args[0]);
     mp_uint_t len = MP_OBJ_SMALL_INT_VALUE(args[1]);
 
-    byte *data;
-    mp_obj_t o = mp_obj_str_builder_start(&mp_type_bytes, len, &data);
+    vstr_t vstr;
+    vstr_init_len(&vstr, len);
+    byte *data = (byte*)vstr.buf;
     memset(data, 0, len);
 
     if (MP_ENDIANNESS_LITTLE) {
@@ -353,7 +354,7 @@ STATIC mp_obj_t int_to_bytes(mp_uint_t n_args, const mp_obj_t *args) {
         }
     }
 
-    return mp_obj_str_builder_end(o);
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(int_to_bytes_obj, 2, 4, int_to_bytes);