py: Refactor slice helpers, preparing to support arbitrary slicing.

py/obj.h

@@ -563,8 +563,16 @@ typedef struct _mp_obj_static_class_method_t {
 const mp_obj_t *mp_obj_property_get(mp_obj_t self_in);
 
 // sequence helpers
+
+// slice indexes resolved to particular sequence
+typedef struct {
+    machine_uint_t start;
+    machine_uint_t stop;
+    machine_int_t step;
+} mp_bound_slice_t;
+
 void mp_seq_multiply(const void *items, uint item_sz, uint len, uint times, void *dest);
-bool mp_seq_get_fast_slice_indexes(machine_uint_t len, mp_obj_t slice, machine_uint_t *begin, machine_uint_t *end);
+bool mp_seq_get_fast_slice_indexes(machine_uint_t len, mp_obj_t slice, mp_bound_slice_t *indexes);
 #define mp_seq_copy(dest, src, len, item_t) memcpy(dest, src, len * sizeof(item_t))
 #define mp_seq_cat(dest, src1, len1, src2, len2, item_t) { memcpy(dest, src1, (len1) * sizeof(item_t)); memcpy(dest + (len1), src2, (len2) * sizeof(item_t)); }
 bool mp_seq_cmp_bytes(int op, const byte *data1, uint len1, const byte *data2, uint len2);

py/objarray.c

@@ -176,15 +176,15 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                 // slice assignment (incl. of different size)
                 return MP_OBJ_NULL; // op not supported
             }
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(o->len, index_in, &start, &stop)) {
+            mp_bound_slice_t slice;
+            if (!mp_seq_get_fast_slice_indexes(o->len, index_in, &slice)) {
                 assert(0);
             }
-            mp_obj_array_t *res = array_new(o->typecode, stop - start);
+            mp_obj_array_t *res = array_new(o->typecode, slice.stop - slice.start);
             int sz = mp_binary_get_size('@', o->typecode, NULL);
             assert(sz > 0);
             byte *p = o->items;
-            memcpy(res->items, p + start * sz, (stop - start) * sz);
+            memcpy(res->items, p + slice.start * sz, (slice.stop - slice.start) * sz);
             return res;
         } else {
             uint index = mp_get_index(o->base.type, o->len, index_in, false);

py/objlist.c

@@ -153,15 +153,15 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
 #if MICROPY_PY_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
             mp_obj_list_t *self = self_in;
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &start, &stop)) {
+            mp_bound_slice_t slice;
+            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
                 assert(0);
             }
 
-            int len_adj = start - stop;
+            int len_adj = slice.start - slice.stop;
             //printf("Len adj: %d\n", len_adj);
             assert(len_adj <= 0);
-            mp_seq_replace_slice_no_grow(self->items, self->len, start, stop, self->items/*NULL*/, 0, mp_obj_t);
+            mp_seq_replace_slice_no_grow(self->items, self->len, slice.start, slice.stop, self->items/*NULL*/, 0, mp_obj_t);
             // 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;
@@ -176,12 +176,12 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         mp_obj_list_t *self = self_in;
 #if MICROPY_PY_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &start, &stop)) {
+            mp_bound_slice_t slice;
+            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
                 assert(0);
             }
-            mp_obj_list_t *res = list_new(stop - start);
-            mp_seq_copy(res->items, self->items + start, res->len, mp_obj_t);
+            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 res;
         }
 #endif
@@ -193,11 +193,11 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
             mp_obj_list_t *self = self_in;
             assert(MP_OBJ_IS_TYPE(value, &mp_type_list));
             mp_obj_list_t *slice = value;
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &start, &stop)) {
+            mp_bound_slice_t slice_out;
+            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice_out)) {
                 assert(0);
             }
-            int len_adj = slice->len - (stop - start);
+            int len_adj = slice->len - (slice_out.stop - slice_out.start);
             //printf("Len adj: %d\n", len_adj);
             if (len_adj > 0) {
                 if (self->len + len_adj > self->alloc) {
@@ -206,9 +206,11 @@ STATIC mp_obj_t list_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
                     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, start, stop, slice->items, slice->len, len_adj, mp_obj_t);
+                mp_seq_replace_slice_grow_inplace(self->items, self->len,
+                    slice_out.start, slice_out.stop, slice->items, slice->len, len_adj, mp_obj_t);
             } else {
-                mp_seq_replace_slice_no_grow(self->items, self->len, start, stop, slice->items, slice->len, mp_obj_t);
+                mp_seq_replace_slice_no_grow(self->items, self->len,
+                    slice_out.start, slice_out.stop, slice->items, slice->len, mp_obj_t);
                 // 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

py/objstr.c

@@ -351,11 +351,11 @@ STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         // load
 #if MICROPY_PY_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(self_len, index, &start, &stop)) {
+            mp_bound_slice_t slice;
+            if (!mp_seq_get_fast_slice_indexes(self_len, index, &slice)) {
                 assert(0);
             }
-            return str_new(type, self_data + start, stop - start);
+            return str_new(type, self_data + slice.start, slice.stop - slice.start);
         }
 #endif
         uint index_val = mp_get_index(type, self_len, index, false);

py/objtuple.c

@@ -163,12 +163,12 @@ mp_obj_t mp_obj_tuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         mp_obj_tuple_t *self = self_in;
 #if MICROPY_PY_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
-            machine_uint_t start, stop;
-            if (!mp_seq_get_fast_slice_indexes(self->len, index, &start, &stop)) {
+            mp_bound_slice_t slice;
+            if (!mp_seq_get_fast_slice_indexes(self->len, index, &slice)) {
                 assert(0);
             }
-            mp_obj_tuple_t *res = mp_obj_new_tuple(stop - start, NULL);
-            mp_seq_copy(res->items, self->items + start, res->len, mp_obj_t);
+            mp_obj_tuple_t *res = mp_obj_new_tuple(slice.stop - slice.start, NULL);
+            mp_seq_copy(res->items, self->items + slice.start, res->len, mp_obj_t);
             return res;
         }
 #endif

py/sequence.c

@@ -51,15 +51,10 @@ void mp_seq_multiply(const void *items, uint item_sz, uint len, uint times, void
     }
 }
 
-bool mp_seq_get_fast_slice_indexes(machine_uint_t len, mp_obj_t slice, machine_uint_t *begin, machine_uint_t *end) {
+bool mp_seq_get_fast_slice_indexes(machine_uint_t len, mp_obj_t slice, mp_bound_slice_t *indexes) {
     mp_obj_t ostart, ostop, ostep;
     machine_int_t start, stop;
     mp_obj_slice_get(slice, &ostart, &ostop, &ostep);
-    if (ostep != mp_const_none && ostep != MP_OBJ_NEW_SMALL_INT(1)) {
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_NotImplementedError,
-            "Only slices with step=1 (aka None) are supported"));
-        return false;
-    }
 
     if (ostart == mp_const_none) {
         start = 0;
@@ -96,8 +91,16 @@ bool mp_seq_get_fast_slice_indexes(machine_uint_t len, mp_obj_t slice, machine_u
         stop = start;
     }
 
-    *begin = start;
-    *end = stop;
+    indexes->start = start;
+    indexes->stop = stop;
+
+    if (ostep != mp_const_none && ostep != MP_OBJ_NEW_SMALL_INT(1)) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_NotImplementedError,
+            "Only slices with step=1 (aka None) are supported"));
+        indexes->step = MP_OBJ_SMALL_INT_VALUE(ostep);
+        return false;
+    }
+    indexes->step = 1;
     return true;
 }