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/*

 * Simple insertion-only 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);

}

void *heap_insert(struct ptr_heap *heap, void *p)

{

        void *res;

        void **ptrs = heap->ptrs;

        int pos;

        if (heap->size < heap->max) {

                /* Heap insertion */

                int 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 */

        res = ptrs[0];

        ptrs[0] = p;

        pos = 0;

        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;

        }

        return res;

}