--- /dev/null
+/*
+ * LICENSING: this file is copied from the Linux kernel. We should therefore
+ * assume a GPLv2 license for the code that comes from the Linux mainline.
+ */
+
+/*
+ * Static-sized priority heap containing pointers. Based on CLR, chapter 7.
+ */
+
+#include <linux/slab.h>
+#include <linux/prio_heap.h>
+
+int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
+ int (*gt)(void *, void *))
+{
+ heap->ptrs = kmalloc(size, gfp_mask);
+ if (!heap->ptrs)
+ return -ENOMEM;
+ heap->size = 0;
+ heap->max = size / sizeof(void *);
+ heap->gt = gt;
+ return 0;
+}
+
+void heap_free(struct ptr_heap *heap)
+{
+ kfree(heap->ptrs);
+}
+
+static void heapify(struct ptr_heap *heap, int pos)
+{
+ void **ptrs = heap->ptrs;
+ void *p = ptrs[pos];
+
+ while (1) {
+ int left = 2 * pos + 1;
+ int right = 2 * pos + 2;
+ int largest = pos;
+ if (left < heap->size && heap->gt(ptrs[left], p))
+ largest = left;
+ if (right < heap->size && heap->gt(ptrs[right], ptrs[largest]))
+ largest = right;
+ if (largest == pos)
+ break;
+ /* Push p down the heap one level and bump one up */
+ ptrs[pos] = ptrs[largest];
+ ptrs[largest] = p;
+ pos = largest;
+ }
+}
+
+void *heap_replace_max(struct ptr_heap *heap, void *p)
+{
+ void *res;
+ void **ptrs = heap->ptrs;
+
+ if (!heap->size) {
+ ptrs[0] = p;
+ heap->size = 1;
+ return NULL;
+ }
+
+ /* Replace the current max and heapify */
+ res = ptrs[0];
+ ptrs[0] = p;
+ heapify(heap, 0);
+ return res;
+}
+
+void *heap_insert(struct ptr_heap *heap, void *p)
+{
+ void **ptrs = heap->ptrs;
+ int pos;
+
+ if (heap->size < heap->max) {
+ /* Heap insertion */
+ pos = heap->size++;
+ while (pos > 0 && heap->gt(p, ptrs[(pos-1)/2])) {
+ ptrs[pos] = ptrs[(pos-1)/2];
+ pos = (pos-1)/2;
+ }
+ ptrs[pos] = p;
+ return NULL;
+ }
+
+ /* The heap is full, so something will have to be dropped */
+
+ /* If the new pointer is greater than the current max, drop it */
+ if (heap->gt(p, ptrs[0]))
+ return p;
+
+ /* Replace the current max and heapify */
+ return heap_replace_max(heap, p);
+}
+
+void *heap_remove(struct ptr_heap *heap)
+{
+ void **ptrs = heap->ptrs;
+
+ switch (heap->size) {
+ case 0:
+ return NULL;
+ case 1:
+ heap->size = 0;
+ return ptrs[0];
+ }
+
+ /* Shrink, replace the current max by previous last entry and heapify */
+ return heap_replace_max(heap, ptrs[--heap->size]);
+}
+
+void *heap_cherrypick(struct ptr_heap *heap, void *p)
+{
+ void **ptrs = heap->ptrs;
+ size_t pos, size = heap->size;
+
+ for (pos = 0; pos < size; pos++)
+ if (ptrs[pos] == p)
+ goto found;
+ return NULL;
+found:
+ if (heap->size == 1) {
+ heap->size = 0;
+ return ptrs[0];
+ }
+ /*
+ * Replace p with previous last entry and heapify.
+ */
+ ptrs[pos] = ptrs[--heap->size];
+ heapify(heap, pos);
+ return p;
+}