| 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 <babeltrace/prio_heap.h> |
| 21 | #include <errno.h> |
| 22 | #include <stdlib.h> |
| 23 | #include <string.h> |
| 24 | |
| 25 | #ifndef max_t |
| 26 | #define max_t(type, a, b) \ |
| 27 | ((type) (a) > (type) (b) ? (type) (a) : (type) (b)) |
| 28 | #endif |
| 29 | |
| 30 | static |
| 31 | size_t parent(size_t i) |
| 32 | { |
| 33 | return i >> 1; |
| 34 | } |
| 35 | |
| 36 | static |
| 37 | size_t left(size_t i) |
| 38 | { |
| 39 | return i << 1; |
| 40 | } |
| 41 | |
| 42 | static |
| 43 | size_t right(size_t i) |
| 44 | { |
| 45 | return (i << 1) + 1; |
| 46 | } |
| 47 | |
| 48 | /* |
| 49 | * Copy of heap->ptrs pointer is invalid after heap_grow. |
| 50 | */ |
| 51 | static |
| 52 | int heap_grow(struct ptr_heap *heap, size_t new_len) |
| 53 | { |
| 54 | void **new_ptrs; |
| 55 | |
| 56 | if (heap->alloc_len >= new_len) |
| 57 | return 0; |
| 58 | |
| 59 | heap->alloc_len = max_t(size_t, new_len, heap->alloc_len << 1); |
| 60 | new_ptrs = calloc(heap->alloc_len, sizeof(void *)); |
| 61 | if (!new_ptrs) |
| 62 | return -ENOMEM; |
| 63 | if (heap->ptrs) |
| 64 | memcpy(new_ptrs, heap->ptrs, heap->len * sizeof(void *)); |
| 65 | free(heap->ptrs); |
| 66 | heap->ptrs = new_ptrs; |
| 67 | return 0; |
| 68 | } |
| 69 | |
| 70 | static |
| 71 | int heap_set_len(struct ptr_heap *heap, size_t new_len) |
| 72 | { |
| 73 | int ret; |
| 74 | |
| 75 | ret = heap_grow(heap, new_len); |
| 76 | if (ret) |
| 77 | return ret; |
| 78 | heap->len = new_len; |
| 79 | return 0; |
| 80 | } |
| 81 | |
| 82 | int heap_init(struct ptr_heap *heap, size_t alloc_len, |
| 83 | int gt(void *a, void *b)) |
| 84 | { |
| 85 | heap->ptrs = NULL; |
| 86 | heap->len = 0; |
| 87 | heap->alloc_len = 0; |
| 88 | heap->gt = gt; |
| 89 | /* |
| 90 | * Minimum size allocated is 1 entry to ensure memory allocation |
| 91 | * never fails within heap_replace_max. |
| 92 | */ |
| 93 | return heap_grow(heap, max_t(size_t, 1, alloc_len)); |
| 94 | } |
| 95 | |
| 96 | void heap_free(struct ptr_heap *heap) |
| 97 | { |
| 98 | free(heap->ptrs); |
| 99 | } |
| 100 | |
| 101 | static void heapify(struct ptr_heap *heap, size_t i) |
| 102 | { |
| 103 | void **ptrs = heap->ptrs; |
| 104 | size_t l, r, largest; |
| 105 | |
| 106 | for (;;) { |
| 107 | l = left(i); |
| 108 | r = right(i); |
| 109 | if (l <= heap->len && ptrs[l] > ptrs[i]) |
| 110 | largest = l; |
| 111 | else |
| 112 | largest = i; |
| 113 | if (r <= heap->len && ptrs[r] > ptrs[largest]) |
| 114 | largest = r; |
| 115 | if (largest != i) { |
| 116 | void *tmp; |
| 117 | |
| 118 | tmp = ptrs[i]; |
| 119 | ptrs[i] = ptrs[largest]; |
| 120 | ptrs[largest] = tmp; |
| 121 | i = largest; |
| 122 | continue; |
| 123 | } else { |
| 124 | break; |
| 125 | } |
| 126 | } |
| 127 | } |
| 128 | |
| 129 | void *heap_replace_max(struct ptr_heap *heap, void *p) |
| 130 | { |
| 131 | void *res; |
| 132 | |
| 133 | if (!heap->len) { |
| 134 | (void) heap_set_len(heap, 1); |
| 135 | heap->ptrs[0] = p; |
| 136 | return NULL; |
| 137 | } |
| 138 | |
| 139 | /* Replace the current max and heapify */ |
| 140 | res = heap->ptrs[0]; |
| 141 | heap->ptrs[0] = p; |
| 142 | heapify(heap, 0); |
| 143 | return res; |
| 144 | } |
| 145 | |
| 146 | int heap_insert(struct ptr_heap *heap, void *p) |
| 147 | { |
| 148 | void **ptrs; |
| 149 | size_t pos; |
| 150 | int ret; |
| 151 | |
| 152 | ret = heap_set_len(heap, heap->len + 1); |
| 153 | if (ret) |
| 154 | return ret; |
| 155 | ptrs = heap->ptrs; |
| 156 | /* Add the element to the end */ |
| 157 | ptrs[heap->len - 1] = p; |
| 158 | pos = heap->len - 1; |
| 159 | /* Bubble it up to the appropriate position. */ |
| 160 | for (;;) { |
| 161 | if (pos > 0 && heap->gt(ptrs[pos], ptrs[parent(pos)])) { |
| 162 | void *tmp; |
| 163 | |
| 164 | /* Need to exchange */ |
| 165 | tmp = ptrs[pos]; |
| 166 | ptrs[pos] = ptrs[parent(pos)]; |
| 167 | ptrs[parent(pos)] = tmp; |
| 168 | pos = parent(pos); |
| 169 | /* |
| 170 | * No need to rebalance: if we are larger than |
| 171 | * our parent, we are necessarily larger than |
| 172 | * its other child. |
| 173 | */ |
| 174 | } else { |
| 175 | break; |
| 176 | } |
| 177 | } |
| 178 | return 0; |
| 179 | } |
| 180 | |
| 181 | void *heap_remove(struct ptr_heap *heap) |
| 182 | { |
| 183 | switch (heap->len) { |
| 184 | case 0: |
| 185 | return NULL; |
| 186 | case 1: |
| 187 | (void) heap_set_len(heap, 0); |
| 188 | return heap->ptrs[0]; |
| 189 | } |
| 190 | /* Shrink, replace the current max by previous last entry and heapify */ |
| 191 | heap_set_len(heap, heap->len - 1); |
| 192 | return heap_replace_max(heap, heap->ptrs[heap->len - 1]); |
| 193 | } |
| 194 | |
| 195 | void *heap_cherrypick(struct ptr_heap *heap, void *p) |
| 196 | { |
| 197 | size_t pos, len = heap->len; |
| 198 | |
| 199 | for (pos = 0; pos < len; pos++) |
| 200 | if (heap->ptrs[pos] == p) |
| 201 | goto found; |
| 202 | return NULL; |
| 203 | found: |
| 204 | if (heap->len == 1) { |
| 205 | (void) heap_set_len(heap, 0); |
| 206 | return heap->ptrs[0]; |
| 207 | } |
| 208 | /* Replace p with previous last entry and heapify. */ |
| 209 | heap_set_len(heap, heap->len - 1); |
| 210 | heap->ptrs[pos] = heap->ptrs[heap->len - 1]; |
| 211 | heapify(heap, pos); |
| 212 | return p; |
| 213 | } |