条件判断还存在问题

src/list.c

@@ -368,6 +368,9 @@ done:
         {
             empty = true;
         }
+
+        if (empty != true)
+        {
             if (start < 0)
             {
                 if (start < -self->size(self))
@@ -420,7 +423,96 @@ done:
         }
         else
         {
+            list = list_new2(self->_obj_size, capacity);
+            if (list == NULL)
+            {
+                return NULL;
+            }
+            list->compare = self->compare;
+            list->print_obj = self->print_obj;
+        }
+    }
+    else
+    {
+        // special case 
+        if (start == LIST_UNLIMITED)
+        {
+            start = self->size(self) - 1;
+        }
+        if (end == LIST_UNLIMITED)
+        {
+            end = 0;
+            contain_last_obj = true;
+        }
 
+        // [start_min, end_max] start > end and limit start_min and end_max
+        if (start <= end || end >= self->size(self) || start < -self->size(self))
+        {
+            empty = true;
+        }
+
+        if (empty != true)
+        {
+            if (start < 0)
+            {
+                if (start < -self->size(self))
+                {
+                    start = -self->size(self);
+                }
+                start += self->size(self);
+            }
+            else
+            {
+                if (start > self->size(self))
+                {
+                    start = self->size(self) - 1;
+                    contain_last_obj = true;
+                }
+            }
+
+            if (end < 0)
+            {
+                end += self->size(self);
+            }
+
+            if (empty != true)
+            {
+                // calc capacity
+                capacity = end - start;
+            }
+            list = list_new2(self->_obj_size, capacity);
+            if (list == NULL)
+            {
+                return NULL;
+            }
+            list->compare = self->compare;
+            list->print_obj = self->print_obj;
+
+            if (contain_last_obj != true)
+            {
+                for (i = start; i > end; i += step)
+                {
+                    list->append(list, (char*)self->obj + i * self->_obj_size);
+                }
+            }
+            else
+            {
+                for (i = start; i >= end; i += step)
+                {
+                    list->append(list, (char*)self->obj + i * self->_obj_size);
+                }
+            }
+        }
+        else
+        {
+            list = list_new2(self->_obj_size, capacity);
+            if (list == NULL)
+            {
+                return NULL;
+            }
+            list->compare = self->compare;
+            list->print_obj = self->print_obj;
+        }
     }
 
     return list;