71 lines
1.4 KiB
C
71 lines
1.4 KiB
C
/*
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* Simple insertion-only static-sized priority heap containing
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* pointers, based on CLR, chapter 7
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*/
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#include <linux/slab.h>
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#include <linux/prio_heap.h>
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int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
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int (*gt)(void *, void *))
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{
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heap->ptrs = kmalloc(size, gfp_mask);
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if (!heap->ptrs)
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return -ENOMEM;
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heap->size = 0;
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heap->max = size / sizeof(void *);
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heap->gt = gt;
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return 0;
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}
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void heap_free(struct ptr_heap *heap)
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{
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kfree(heap->ptrs);
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}
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void *heap_insert(struct ptr_heap *heap, void *p)
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{
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void *res;
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void **ptrs = heap->ptrs;
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int pos;
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if (heap->size < heap->max) {
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/* Heap insertion */
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pos = heap->size++;
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while (pos > 0 && heap->gt(p, ptrs[(pos-1)/2])) {
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ptrs[pos] = ptrs[(pos-1)/2];
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pos = (pos-1)/2;
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}
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ptrs[pos] = p;
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return NULL;
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}
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/* The heap is full, so something will have to be dropped */
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/* If the new pointer is greater than the current max, drop it */
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if (heap->gt(p, ptrs[0]))
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return p;
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/* Replace the current max and heapify */
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res = ptrs[0];
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ptrs[0] = p;
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pos = 0;
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while (1) {
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int left = 2 * pos + 1;
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int right = 2 * pos + 2;
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int largest = pos;
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if (left < heap->size && heap->gt(ptrs[left], p))
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largest = left;
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if (right < heap->size && heap->gt(ptrs[right], ptrs[largest]))
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largest = right;
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if (largest == pos)
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break;
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/* Push p down the heap one level and bump one up */
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ptrs[pos] = ptrs[largest];
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ptrs[largest] = p;
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pos = largest;
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}
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return res;
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}
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