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.

2 files changed, 8 insertions, 7 deletions

diff --git a/extmod/modubinascii.c b/extmod/modubinascii.c
index de8b5d9aeb..e258818af4 100644
--- a/extmod/modubinascii.c
+++ b/extmod/modubinascii.c
@@ -39,8 +39,9 @@ STATIC mp_obj_t mod_binascii_hexlify(mp_uint_t n_args, const mp_obj_t *args) {
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[0], &bufinfo, MP_BUFFER_READ);
 
-    byte *in = bufinfo.buf, *out;
-    mp_obj_t o = mp_obj_str_builder_start(&mp_type_bytes, bufinfo.len * 2, &out);
+    vstr_t vstr;
+    vstr_init_len(&vstr, bufinfo.len * 2);
+    byte *in = bufinfo.buf, *out = (byte*)vstr.buf;
     for (mp_uint_t i = bufinfo.len; i--;) {
         byte d = (*in >> 4);
         if (d > 9) {
@@ -53,7 +54,7 @@ STATIC mp_obj_t mod_binascii_hexlify(mp_uint_t n_args, const mp_obj_t *args) {
         }
         *out++ = d + '0';
     }
-    return mp_obj_str_builder_end(o);
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_binascii_hexlify_obj, 1, 2, mod_binascii_hexlify);
 
diff --git a/extmod/moduhashlib.c b/extmod/moduhashlib.c
index 40a0f06094..e9100fa1b6 100644
--- a/extmod/moduhashlib.c
+++ b/extmod/moduhashlib.c
@@ -63,10 +63,10 @@ MP_DEFINE_CONST_FUN_OBJ_2(hash_update_obj, hash_update);
 
 STATIC mp_obj_t hash_digest(mp_obj_t self_in) {
     mp_obj_hash_t *self = self_in;
-    byte *hash;
-    mp_obj_t o = mp_obj_str_builder_start(&mp_type_bytes, SHA256_BLOCK_SIZE, &hash);
-    sha256_final((SHA256_CTX*)self->state, hash);
-    return mp_obj_str_builder_end(o);
+    vstr_t vstr;
+    vstr_init_len(&vstr, SHA256_BLOCK_SIZE);
+    sha256_final((SHA256_CTX*)self->state, (byte*)vstr.buf);
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 MP_DEFINE_CONST_FUN_OBJ_1(hash_digest_obj, hash_digest);