prio-queue: priority queue of pointers to structs

[thirdparty/git.git] / prio-queue.c

diff --git a/prio-queue.c b/prio-queue.c
new file mode 100644 (file)
index 0000000..f2a4973
--- /dev/null
+++ b/prio-queue.c
@@ -0,0 +1,71 @@
+#include "cache.h"
+#include "commit.h"
+#include "prio-queue.h"
+
+void clear_prio_queue(struct prio_queue *queue)
+{
+       free(queue->array);
+       queue->nr = 0;
+       queue->alloc = 0;
+       queue->array = NULL;
+}
+
+void prio_queue_put(struct prio_queue *queue, void *thing)
+{
+       prio_queue_compare_fn compare = queue->compare;
+       int ix, parent;
+
+       /* Append at the end */
+       ALLOC_GROW(queue->array, queue->nr + 1, queue->alloc);
+       queue->array[queue->nr++] = thing;
+       if (!compare)
+               return; /* LIFO */
+
+       /* Bubble up the new one */
+       for (ix = queue->nr - 1; ix; ix = parent) {
+               parent = (ix - 1) / 2;
+               if (compare(queue->array[parent], queue->array[ix],
+                           queue->cb_data) <= 0)
+                       break;
+
+               thing = queue->array[parent];
+               queue->array[parent] = queue->array[ix];
+               queue->array[ix] = thing;
+       }
+}
+
+void *prio_queue_get(struct prio_queue *queue)
+{
+       void *result, *swap;
+       int ix, child;
+       prio_queue_compare_fn compare = queue->compare;
+
+       if (!queue->nr)
+               return NULL;
+       if (!compare)
+               return queue->array[--queue->nr]; /* LIFO */
+
+       result = queue->array[0];
+       if (!--queue->nr)
+               return result;
+
+       queue->array[0] = queue->array[queue->nr];
+
+       /* Push down the one at the root */
+       for (ix = 0; ix * 2 + 1 < queue->nr; ix = child) {
+               child = ix * 2 + 1; /* left */
+               if ((child + 1 < queue->nr) &&
+                   (compare(queue->array[child], queue->array[child + 1],
+                            queue->cb_data) >= 0))
+                       child++; /* use right child */
+
+               if (compare(queue->array[ix], queue->array[child],
+                           queue->cb_data) <= 0)
+                       break;
+
+               swap = queue->array[child];
+               queue->array[child] = queue->array[ix];
+               queue->array[ix] = swap;
+       }
+       return result;
+}