| 1 | /* |
| 2 | * prio_heap.c |
| 3 | * |
| 4 | * Static-sized priority heap containing pointers. Based on CLRS, |
| 5 | * chapter 6. |
| 6 | * |
| 7 | * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 8 | * |
| 9 | * Permission is hereby granted, free of charge, to any person obtaining a copy |
| 10 | * of this software and associated documentation files (the "Software"), to deal |
| 11 | * in the Software without restriction, including without limitation the rights |
| 12 | * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
| 13 | * copies of the Software, and to permit persons to whom the Software is |
| 14 | * furnished to do so, subject to the following conditions: |
| 15 | * |
| 16 | * The above copyright notice and this permission notice shall be included in |
| 17 | * all copies or substantial portions of the Software. |
| 18 | */ |
| 19 | |
| 20 | #include <linux/slab.h> |
| 21 | #include <linux/prio_heap.h> |
| 22 | |
| 23 | int heap_init(struct ptr_heap *heap, size_t size, |
| 24 | gfp_t gfpmask, int gt(void *a, void *b)) |
| 25 | { |
| 26 | WARN_ON_ONCE(size == 0); |
| 27 | heap->ptrs = kmalloc(size * sizeof(void *), gfpmask); |
| 28 | if (!heap->ptrs) |
| 29 | return -ENOMEM; |
| 30 | heap->size = 0; |
| 31 | heap->max = size; |
| 32 | heap->gt = gt; |
| 33 | return 0; |
| 34 | } |
| 35 | |
| 36 | void heap_free(struct ptr_heap *heap) |
| 37 | { |
| 38 | kfree(heap->ptrs); |
| 39 | } |
| 40 | |
| 41 | static void heapify(struct ptr_heap *heap, int pos) |
| 42 | { |
| 43 | void **ptrs = heap->ptrs; |
| 44 | void *p = ptrs[pos]; |
| 45 | |
| 46 | while (1) { |
| 47 | int left = 2 * pos + 1; |
| 48 | int right = 2 * pos + 2; |
| 49 | int largest = pos; |
| 50 | if (left < heap->size && heap->gt(ptrs[left], p)) |
| 51 | largest = left; |
| 52 | if (right < heap->size && heap->gt(ptrs[right], ptrs[largest])) |
| 53 | largest = right; |
| 54 | if (largest == pos) |
| 55 | break; |
| 56 | /* Push p down the heap one level and bump one up */ |
| 57 | ptrs[pos] = ptrs[largest]; |
| 58 | ptrs[largest] = p; |
| 59 | pos = largest; |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | void *heap_replace_max(struct ptr_heap *heap, void *p) |
| 64 | { |
| 65 | void *res; |
| 66 | void **ptrs = heap->ptrs; |
| 67 | |
| 68 | if (!heap->size) { |
| 69 | ptrs[0] = p; |
| 70 | heap->size = 1; |
| 71 | return NULL; |
| 72 | } |
| 73 | |
| 74 | /* Replace the current max and heapify */ |
| 75 | res = ptrs[0]; |
| 76 | ptrs[0] = p; |
| 77 | heapify(heap, 0); |
| 78 | return res; |
| 79 | } |
| 80 | |
| 81 | void *heap_insert(struct ptr_heap *heap, void *p) |
| 82 | { |
| 83 | void **ptrs = heap->ptrs; |
| 84 | void *tmp = NULL; |
| 85 | |
| 86 | if (heap->size < heap->max) { |
| 87 | /* Add the element to the end */ |
| 88 | heap->ptrs[heap->size++] = p; |
| 89 | /* rebalance */ |
| 90 | heapify(heap, 0); |
| 91 | return NULL; |
| 92 | } |
| 93 | |
| 94 | /* |
| 95 | * Full. We need to replace the largest (if we are |
| 96 | * smaller or equal to this element). |
| 97 | */ |
| 98 | if (heap->gt(ptrs[0], p)) { |
| 99 | tmp = ptrs[0]; |
| 100 | ptrs[0] = p; |
| 101 | /* rebalance */ |
| 102 | heapify(heap, 0); |
| 103 | } else { |
| 104 | tmp = p; |
| 105 | } |
| 106 | return tmp; |
| 107 | } |
| 108 | |
| 109 | void *heap_remove(struct ptr_heap *heap) |
| 110 | { |
| 111 | void **ptrs = heap->ptrs; |
| 112 | |
| 113 | switch (heap->size) { |
| 114 | case 0: |
| 115 | return NULL; |
| 116 | case 1: |
| 117 | heap->size = 0; |
| 118 | return ptrs[0]; |
| 119 | } |
| 120 | |
| 121 | /* Shrink, replace the current max by previous last entry and heapify */ |
| 122 | return heap_replace_max(heap, ptrs[--heap->size]); |
| 123 | } |
| 124 | |
| 125 | void *heap_cherrypick(struct ptr_heap *heap, void *p) |
| 126 | { |
| 127 | void **ptrs = heap->ptrs; |
| 128 | size_t pos, size = heap->size; |
| 129 | |
| 130 | for (pos = 0; pos < size; pos++) |
| 131 | if (ptrs[pos] == p) |
| 132 | goto found; |
| 133 | return NULL; |
| 134 | found: |
| 135 | if (heap->size == 1) { |
| 136 | heap->size = 0; |
| 137 | return ptrs[0]; |
| 138 | } |
| 139 | /* |
| 140 | * Replace p with previous last entry and heapify. |
| 141 | */ |
| 142 | ptrs[pos] = ptrs[--heap->size]; |
| 143 | heapify(heap, pos); |
| 144 | return p; |
| 145 | } |