py/objlist: Reduce code size in slice operations.

By refactoring the code to separate out the slicing operation from the
regular indexing operation, code can be shared between the various types of
slice operations (read/assign/delete).

Signed-off-by: Jeff Epler <[email protected]>

Author: jepler

py/objlist.c

@@ -159,76 +159,63 @@ static mp_obj_t list_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
 }
 
 static mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
-    if (value == MP_OBJ_NULL) {
-        // delete
-        #if MICROPY_PY_BUILTINS_SLICE
-        if (mp_obj_is_type(index, &mp_type_slice)) {
-            mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
-            mp_bound_slice_t slice;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
-                mp_raise_NotImplementedError(NULL);
+    #if MICROPY_PY_BUILTINS_SLICE
+    if (mp_obj_is_type(index, &mp_type_slice)) {
+        mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
+        mp_bound_slice_t slice;
+        bool fast = mp_seq_get_fast_slice_indexes(self->len, index, &slice);
+        if (value == MP_OBJ_SENTINEL) {
+            // load
+            if (!fast) {
+                return mp_seq_extract_slice(self->items, &slice);
             }
-
-            mp_int_t len_adj = slice.start - slice.stop;
-            assert(len_adj <= 0);
-            mp_seq_replace_slice_no_grow(self->items, self->len, slice.start, slice.stop, self->items /*NULL*/, 0, sizeof(*self->items));
+            mp_obj_list_t *res = list_new(slice.stop - slice.start);
+            mp_seq_copy(res->items, self->items + slice.start, res->len, mp_obj_t);
+            return MP_OBJ_FROM_PTR(res);
+        }
+        // assign/delete
+        if (value == MP_OBJ_NULL) {
+            // delete is equivalent to slice assignment of an empty sequence
+            value = mp_const_empty_tuple;
+        }
+        if (!fast) {
+            mp_raise_NotImplementedError(NULL);
+        }
+        size_t value_len;
+        mp_obj_t *value_items;
+        mp_obj_get_array(value, &value_len, &value_items);
+        mp_int_t len_adj = value_len - (slice.stop - slice.start);
+        if (len_adj > 0) {
+            if (self->len + len_adj > self->alloc) {
+                // TODO: Might optimize memory copies here by checking if block can
+                // be grown inplace or not
+                self->items = m_renew(mp_obj_t, self->items, self->alloc, self->len + len_adj);
+                self->alloc = self->len + len_adj;
+            }
+            mp_seq_replace_slice_grow_inplace(self->items, self->len,
+                slice.start, slice.stop, value_items, value_len, len_adj, sizeof(*self->items));
+        } else {
+            mp_seq_replace_slice_no_grow(self->items, self->len,
+                slice.start, slice.stop, value_items, value_len, sizeof(*self->items));
             // Clear "freed" elements at the end of list
             mp_seq_clear(self->items, self->len + len_adj, self->len, sizeof(*self->items));
-            self->len += len_adj;
-            return mp_const_none;
+            // TODO: apply allocation policy re: alloc_size
         }
-        #endif
+        self->len += len_adj;
+        return mp_const_none;
+    }
+    #endif
+    if (value == MP_OBJ_NULL) {
+        // delete
         mp_obj_t args[2] = {self_in, index};
         list_pop(2, args);
         return mp_const_none;
     } else if (value == MP_OBJ_SENTINEL) {
         // load
         mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
-        #if MICROPY_PY_BUILTINS_SLICE
-        if (mp_obj_is_type(index, &mp_type_slice)) {
-            mp_bound_slice_t slice;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
-                return mp_seq_extract_slice(self->items, &slice);
-            }
-            mp_obj_list_t *res = list_new(slice.stop - slice.start);
-            mp_seq_copy(res->items, self->items + slice.start, res->len, mp_obj_t);
-            return MP_OBJ_FROM_PTR(res);
-        }
-        #endif
         size_t index_val = mp_get_index(self->base.type, self->len, index, false);
         return self->items[index_val];
     } else {
-        #if MICROPY_PY_BUILTINS_SLICE
-        if (mp_obj_is_type(index, &mp_type_slice)) {
-            mp_obj_list_t *self = MP_OBJ_TO_PTR(self_in);
-            size_t value_len;
-            mp_obj_t *value_items;
-            mp_obj_get_array(value, &value_len, &value_items);
-            mp_bound_slice_t slice_out;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice_out)) {
-                mp_raise_NotImplementedError(NULL);
-            }
-            mp_int_t len_adj = value_len - (slice_out.stop - slice_out.start);
-            if (len_adj > 0) {
-                if (self->len + len_adj > self->alloc) {
-                    // TODO: Might optimize memory copies here by checking if block can
-                    // be grown inplace or not
-                    self->items = m_renew(mp_obj_t, self->items, self->alloc, self->len + len_adj);
-                    self->alloc = self->len + len_adj;
-                }
-                mp_seq_replace_slice_grow_inplace(self->items, self->len,
-                    slice_out.start, slice_out.stop, value_items, value_len, len_adj, sizeof(*self->items));
-            } else {
-                mp_seq_replace_slice_no_grow(self->items, self->len,
-                    slice_out.start, slice_out.stop, value_items, value_len, sizeof(*self->items));
-                // Clear "freed" elements at the end of list
-                mp_seq_clear(self->items, self->len + len_adj, self->len, sizeof(*self->items));
-                // TODO: apply allocation policy re: alloc_size
-            }
-            self->len += len_adj;
-            return mp_const_none;
-        }
-        #endif
         mp_obj_list_store(self_in, index, value);
         return mp_const_none;
     }