linked-list reverse iteration (#343)

awslabs · May 9, 2019 · f0a8edf · f0a8edf
1 parent 534c7f2
commit f0a8edf
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diff --git a/include/aws/common/linked_list.h b/include/aws/common/linked_list.h
@@ -69,13 +69,37 @@ AWS_STATIC_IMPL const struct aws_linked_list_node *aws_linked_list_end(const str
     return &list->tail;
 }
 
+/**
+ * Returns a pointer for the last element in the list.
+ * Used to begin iterating the list in reverse. Ex:
+ *   for (i = aws_linked_list_rbegin(list); i != aws_linked_list_rend(list); i = aws_linked_list_prev(i)) {...}
+ */
+AWS_STATIC_IMPL struct aws_linked_list_node *aws_linked_list_rbegin(const struct aws_linked_list *list) {
+    return list->tail.prev;
+}
+
+/**
+ * Returns the pointer to one before the first element in the list.
+ * Used to end iterating the list in reverse.
+ */
+AWS_STATIC_IMPL const struct aws_linked_list_node *aws_linked_list_rend(const struct aws_linked_list *list) {
+    return &list->head;
+}
+
 /**
  * Returns the next element in the list.
  */
 AWS_STATIC_IMPL struct aws_linked_list_node *aws_linked_list_next(const struct aws_linked_list_node *node) {
     return node->next;
 }
 
+/**
+ * Returns the previous element in the list.
+ */
+AWS_STATIC_IMPL struct aws_linked_list_node *aws_linked_list_prev(const struct aws_linked_list_node *node) {
+    return node->prev;
+}
+
 /**
  * Inserts to_add immediately after after.
  */

diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
@@ -81,6 +81,7 @@ add_test_case(priority_queue_remove_interior_sift_down_test)
 add_test_case(linked_list_push_back_pop_front)
 add_test_case(linked_list_push_front_pop_back)
 add_test_case(linked_list_iteration)
+add_test_case(linked_list_reverse_iteration)
 add_test_case(linked_list_swap_contents)
 
 add_test_case(hex_encoding_test_case_empty_test)

diff --git a/tests/linked_list_test.c b/tests/linked_list_test.c
@@ -115,6 +115,7 @@ static int s_test_linked_list_iteration(struct aws_allocator *allocator, void *c
     aws_linked_list_init(&list);
 
     ASSERT_TRUE(aws_linked_list_empty(&list));
+    ASSERT_PTR_EQUALS(aws_linked_list_begin(&list), aws_linked_list_end(&list));
 
     struct int_value first = (struct int_value){.value = 1};
     struct int_value second = (struct int_value){.value = 2};
@@ -127,6 +128,7 @@ static int s_test_linked_list_iteration(struct aws_allocator *allocator, void *c
     aws_linked_list_push_back(&list, &fourth.node);
 
     ASSERT_FALSE(aws_linked_list_empty(&list));
+    ASSERT_FALSE(aws_linked_list_begin(&list) == aws_linked_list_end(&list));
 
     int count = 1;
     for (struct aws_linked_list_node *iter = aws_linked_list_begin(&list); iter != aws_linked_list_end(&list);
@@ -140,6 +142,42 @@ static int s_test_linked_list_iteration(struct aws_allocator *allocator, void *c
     return 0;
 }
 
+static int s_test_linked_list_reverse_iteration(struct aws_allocator *allocator, void *ctx) {
+    (void)allocator;
+    (void)ctx;
+
+    struct aws_linked_list list;
+
+    aws_linked_list_init(&list);
+
+    ASSERT_TRUE(aws_linked_list_empty(&list));
+    ASSERT_PTR_EQUALS(aws_linked_list_rbegin(&list), aws_linked_list_rend(&list));
+
+    struct int_value first = (struct int_value){.value = 1};
+    struct int_value second = (struct int_value){.value = 2};
+    struct int_value third = (struct int_value){.value = 3};
+    struct int_value fourth = (struct int_value){.value = 4};
+
+    aws_linked_list_push_back(&list, &first.node);
+    aws_linked_list_push_back(&list, &second.node);
+    aws_linked_list_push_back(&list, &third.node);
+    aws_linked_list_push_back(&list, &fourth.node);
+
+    ASSERT_FALSE(aws_linked_list_empty(&list));
+    ASSERT_FALSE(aws_linked_list_rbegin(&list) == aws_linked_list_rend(&list));
+
+    int count = 4;
+    for (struct aws_linked_list_node *iter = aws_linked_list_rbegin(&list); iter != aws_linked_list_rend(&list);
+         iter = aws_linked_list_prev(iter)) {
+
+        int item = AWS_CONTAINER_OF(iter, struct int_value, node)->value;
+        ASSERT_INT_EQUALS(count, item);
+        --count;
+    }
+
+    return 0;
+}
+
 static int s_test_linked_list_swap_contents(struct aws_allocator *allocator, void *ctx) {
     (void)allocator;
     (void)ctx;
@@ -232,4 +270,5 @@ static int s_test_linked_list_swap_contents(struct aws_allocator *allocator, voi
 AWS_TEST_CASE(linked_list_push_back_pop_front, s_test_linked_list_order_push_back_pop_front)
 AWS_TEST_CASE(linked_list_push_front_pop_back, s_test_linked_list_order_push_front_pop_back)
 AWS_TEST_CASE(linked_list_iteration, s_test_linked_list_iteration)
+AWS_TEST_CASE(linked_list_reverse_iteration, s_test_linked_list_reverse_iteration)
 AWS_TEST_CASE(linked_list_swap_contents, s_test_linked_list_swap_contents)