py: Simplify bytecode prelude when encoding closed over variables.

3 files changed, 8 insertions, 16 deletions

diff --git a/py/bc.c b/py/bc.c
index af855e9474..865065ab19 100644
--- a/py/bc.c
+++ b/py/bc.c
@@ -228,9 +228,10 @@ continue2:;
 
     // bytecode prelude: initialise closed over variables
     const byte *ip = code_state->ip;
-    for (mp_uint_t n_local = *ip++; n_local > 0; n_local--) {
-        mp_uint_t local_num = *ip++;
-        code_state->state[n_state - 1 - local_num] = mp_obj_new_cell(code_state->state[n_state - 1 - local_num]);
+    mp_uint_t local_num;
+    while ((local_num = *ip++) != 255) {
+        code_state->state[n_state - 1 - local_num] =
+            mp_obj_new_cell(code_state->state[n_state - 1 - local_num]);
     }
 
     // now that we skipped over the prelude, set the ip for the VM
diff --git a/py/emitbc.c b/py/emitbc.c
index 70267bd7cc..f55fa964be 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -322,21 +322,14 @@ void mp_emit_bc_start_pass(emit_t *emit, pass_kind_t pass, scope_t *scope) {
     }
 
     // bytecode prelude: initialise closed over variables
-    int num_cell = 0;
-    for (int i = 0; i < scope->id_info_len; i++) {
-        id_info_t *id = &scope->id_info[i];
-        if (id->kind == ID_INFO_KIND_CELL) {
-            num_cell += 1;
-        }
-    }
-    assert(num_cell <= 255);
-    emit_write_bytecode_byte(emit, num_cell); // write number of locals that are cells
     for (int i = 0; i < scope->id_info_len; i++) {
         id_info_t *id = &scope->id_info[i];
         if (id->kind == ID_INFO_KIND_CELL) {
+            assert(id->local_num < 255);
             emit_write_bytecode_byte(emit, id->local_num); // write the local which should be converted to a cell
         }
     }
+    emit_write_bytecode_byte(emit, 255); // end of list sentinel
 }
 
 void mp_emit_bc_end_pass(emit_t *emit) {
diff --git a/py/showbc.c b/py/showbc.c
index 3a468326db..c9eeaff9fa 100644
--- a/py/showbc.c
+++ b/py/showbc.c
@@ -95,10 +95,8 @@ void mp_bytecode_print(const void *descr, mp_uint_t n_total_args, const byte *ip
 
     // bytecode prelude: initialise closed over variables
     {
-        uint n_local = *ip++;
-        printf("(NUM_LOCAL %u)\n", n_local);
-        for (; n_local > 0; n_local--) {
-            uint local_num = *ip++;
+        uint local_num;
+        while ((local_num = *ip++) != 255) {
             printf("(INIT_CELL %u)\n", local_num);
         }
         len -= ip - mp_showbc_code_start;