The ABT data structure partially abstracts augmentation. The
client passes in a "reaugmentation" function that accepts a
- node and its left and right children. This function must
- recalculate the node's augmentation data based on its own
- contents and the contents of its children, and store the new
- augmentation data in the node.
+ node. This function must recalculate the node's augmentation
+ data based on its own contents and the contents of its
+ children, and store the new augmentation data in the node.
The ABT automatically calls the reaugmentation function
whenever it can tell that a node's augmentation data might
static struct element *
node_to_element (const struct abt_node *node)
{
- return abt_data (node, struct element, node);
+ return ABT_DATA (node, struct element, node);
}
// Compares the DATA values in A and B and returns a
}
// Recalculates the count for NODE's subtree by adding up the
- // counts for its LEFT and RIGHT child subtrees.
+ // counts for its left and right child subtrees.
static void
- reaugment_elements (struct abt_node *node_,
- const struct abt_node *left,
- const struct abt_node *right,
- const void *aux)
+ reaugment_elements (struct abt_node *node_, const void *aux)
{
struct element *node = node_to_element (node_);
node->count = 1;
- if (left != NULL)
- node->count += node_to_element (left)->count;
- if (right != NULL)
- node->count += node_to_element (right)->count;
+ if (node->node.down[0] != NULL)
+ node->count += node_to_element (node->node.down[0])->count;
+ if (node->node.down[1] != NULL)
+ node->count += node_to_element (node->node.down[1])->count;
}
// Finds and returns the element in ABT that is in the given
find_by_position (struct abt *abt, int position)
{
struct abt_node *p;
- for (p = abt->root; p != NULL; )
+ for (p = abt->root; p != NULL;)
{
int p_pos = p->down[0] ? node_to_element (p->down[0])->count : 0;
if (position == p_pos)
code and links to other resources, such as the original AA
tree paper. */
+#include <stdbool.h>
#include <stddef.h>
#include "libpspp/cast.h"
-/* Returns the data structure corresponding to the given NODE,
- assuming that NODE is embedded as the given MEMBER name in
- data type STRUCT. */
-#define abt_data(NODE, STRUCT, MEMBER) \
- (CHECK_POINTER_HAS_TYPE (NODE, struct abt_node *), \
- UP_CAST (NODE, STRUCT, MEMBER))
+/* Returns the data structure corresponding to the given NODE, assuming that
+ NODE is embedded as the given MEMBER name in data type STRUCT. NODE must
+ not be a null pointer. */
+#define ABT_DATA(NODE, STRUCT, MEMBER) \
+ (CHECK_POINTER_HAS_TYPE (NODE, struct abt_node *), \
+ UP_CAST (NODE, STRUCT, MEMBER))
+
+/* Like ABT_DATA, except that a null NODE yields a null pointer result. */
+#define ABT_NULLABLE_DATA(NODE, STRUCT, MEMBER) \
+ ((STRUCT *) abt_nullable_data__ (NODE, offsetof (STRUCT, MEMBER)))
/* Node in an augmented binary tree. */
struct abt_node
const struct abt_node *b,
const void *aux);
-/* Recalculates NODE's augmentation based on NODE's data and that
- of its LEFT and RIGHT children, with the tree's AUX. */
-typedef void abt_reaugment_func (struct abt_node *node,
- const struct abt_node *left,
- const struct abt_node *right,
- const void *aux);
+/* Recalculates NODE's augmentation based on NODE's data and that of its left
+ and right children NODE->down[0] and NODE[1], respectively, with the tree's
+ AUX. */
+typedef void abt_reaugment_func (struct abt_node *node, const void *aux);
/* An augmented binary tree. */
struct abt
abt_reaugment_func *reaugment; /* To augment a node using its children. */
const void *aux; /* Auxiliary data. */
};
+#define ABT_INITIALIZER(COMPARE, REAUGMENT, AUX) \
+ { .compare = COMPARE, .reaugment = REAUGMENT, .aux = AUX }
void abt_init (struct abt *, abt_compare_func *, abt_reaugment_func *,
const void *aux);
+static inline bool abt_is_empty (const struct abt *);
+
struct abt_node *abt_insert (struct abt *, struct abt_node *);
void abt_insert_after (struct abt *,
const struct abt_node *, struct abt_node *);
struct abt_node *abt_changed (struct abt *, struct abt_node *);
void abt_moved (struct abt *, struct abt_node *);
+/* Convenience macros for iteration.
+
+ These macros automatically use ABT_DATA to obtain the data elements that
+ encapsulate abt nodes, which often saves typing and can make code easier to
+ read. Refer to the large comment near the top of this file for an example.
+
+ These macros evaluate their arguments many times. */
+#define ABT_FIRST(STRUCT, MEMBER, ABT) \
+ ABT_NULLABLE_DATA (abt_first (ABT), STRUCT, MEMBER)
+#define ABT_NEXT(DATA, STRUCT, MEMBER, ABT) \
+ ABT_NULLABLE_DATA (abt_next (ABT, &(DATA)->MEMBER), STRUCT, MEMBER)
+#define ABT_FOR_EACH(DATA, STRUCT, MEMBER, ABT) \
+ for ((DATA) = ABT_FIRST (STRUCT, MEMBER, ABT); \
+ (DATA) != NULL; \
+ (DATA) = ABT_NEXT (DATA, STRUCT, MEMBER, ABT))
+#define ABT_FOR_EACH_SAFE(DATA, NEXT, STRUCT, MEMBER, ABT) \
+ for ((DATA) = ABT_FIRST (STRUCT, MEMBER, ABT); \
+ ((DATA) != NULL \
+ ? ((NEXT) = ABT_NEXT (DATA, STRUCT, MEMBER, ABT), 1) \
+ : 0); \
+ (DATA) = (NEXT))
+
+/* Returns true if ABT contains no nodes, false if ABT contains at least one
+ node. */
+static inline bool
+abt_is_empty (const struct abt *abt)
+{
+ return abt->root == NULL;
+}
+
+/* Helper for ABT_NULLABLE_DATA (to avoid evaluating its NODE argument more
+ than once). */
+static inline void *
+abt_nullable_data__ (struct abt_node *node, size_t member_offset)
+{
+ return node != NULL ? (char *) node - member_offset : NULL;
+}
+
#endif /* libpspp/abt.h */
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