lib/prio_heap/prio_heap.c

   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  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  22  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  25  * SOFTWARE.
  26  */
  27
  28 #include <babeltrace/prio-heap-internal.h>
  29 #include <babeltrace/babeltrace-internal.h>
  30 #include <errno.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <assert.h>
  34
  35 #ifdef DEBUG_HEAP
  36 void check_heap(const struct ptr_heap *heap)
  37 {
  38         size_t i;
  39
  40         if (!heap->len)
  41                 return;
  42
  43         for (i = 1; i < heap->len; i++)
  44                 assert(!heap->gt(heap->ptrs[i], heap->ptrs[0]));
  45 }
  46 #endif
  47
  48 static
  49 size_t parent(size_t i)
  50 {
  51         return (i - 1) >> 1;
  52 }
  53
  54 static
  55 size_t left(size_t i)
  56 {
  57         return (i << 1) + 1;
  58 }
  59
  60 static
  61 size_t right(size_t i)
  62 {
  63         return (i << 1) + 2;
  64 }
  65
  66 /*
  67  * Copy of heap->ptrs pointer is invalid after heap_grow.
  68  */
  69 static
  70 int heap_grow(struct ptr_heap *heap, size_t new_len)
  71 {
  72         void **new_ptrs;
  73
  74         if (likely(heap->alloc_len >= new_len))
  75                 return 0;
  76
  77         heap->alloc_len = max_t(size_t, new_len, heap->alloc_len << 1);
  78         new_ptrs = calloc(heap->alloc_len, sizeof(void *));
  79         if (unlikely(!new_ptrs))
  80                 return -ENOMEM;
  81         if (likely(heap->ptrs))
  82                 memcpy(new_ptrs, heap->ptrs, heap->len * sizeof(void *));
  83         free(heap->ptrs);
  84         heap->ptrs = new_ptrs;
  85         return 0;
  86 }
  87
  88 static
  89 int heap_set_len(struct ptr_heap *heap, size_t new_len)
  90 {
  91         int ret;
  92
  93         ret = heap_grow(heap, new_len);
  94         if (unlikely(ret))
  95                 return ret;
  96         heap->len = new_len;
  97         return 0;
  98 }
  99
 100 int bt_heap_init(struct ptr_heap *heap, size_t alloc_len,
 101               int gt(void *a, void *b))
 102 {
 103         heap->ptrs = NULL;
 104         heap->len = 0;
 105         heap->alloc_len = 0;
 106         heap->gt = gt;
 107         /*
 108          * Minimum size allocated is 1 entry to ensure memory allocation
 109          * never fails within bt_heap_replace_max.
 110          */
 111         return heap_grow(heap, max_t(size_t, 1, alloc_len));
 112 }
 113
 114 void bt_heap_free(struct ptr_heap *heap)
 115 {
 116         free(heap->ptrs);
 117 }
 118
 119 static void heapify(struct ptr_heap *heap, size_t i)
 120 {
 121         void **ptrs = heap->ptrs;
 122         size_t l, r, largest;
 123
 124         for (;;) {
 125                 void *tmp;
 126
 127                 l = left(i);
 128                 r = right(i);
 129                 if (l < heap->len && heap->gt(ptrs[l], ptrs[i]))
 130                         largest = l;
 131                 else
 132                         largest = i;
 133                 if (r < heap->len && heap->gt(ptrs[r], ptrs[largest]))
 134                         largest = r;
 135                 if (unlikely(largest == i))
 136                         break;
 137                 tmp = ptrs[i];
 138                 ptrs[i] = ptrs[largest];
 139                 ptrs[largest] = tmp;
 140                 i = largest;
 141         }
 142         check_heap(heap);
 143 }
 144
 145 void *bt_heap_replace_max(struct ptr_heap *heap, void *p)
 146 {
 147         void *res;
 148
 149         if (unlikely(!heap->len)) {
 150                 (void) heap_set_len(heap, 1);
 151                 heap->ptrs[0] = p;
 152                 check_heap(heap);
 153                 return NULL;
 154         }
 155
 156         /* Replace the current max and heapify */
 157         res = heap->ptrs[0];
 158         heap->ptrs[0] = p;
 159         heapify(heap, 0);
 160         return res;
 161 }
 162
 163 int bt_heap_insert(struct ptr_heap *heap, void *p)
 164 {
 165         void **ptrs;
 166         size_t pos;
 167         int ret;
 168
 169         ret = heap_set_len(heap, heap->len + 1);
 170         if (unlikely(ret))
 171                 return ret;
 172         ptrs = heap->ptrs;
 173         pos = heap->len - 1;
 174         while (pos > 0 && heap->gt(p, ptrs[parent(pos)])) {
 175                 /* Move parent down until we find the right spot */
 176                 ptrs[pos] = ptrs[parent(pos)];
 177                 pos = parent(pos);
 178         }
 179         ptrs[pos] = p;
 180         check_heap(heap);
 181         return 0;
 182 }
 183
 184 void *bt_heap_remove(struct ptr_heap *heap)
 185 {
 186         switch (heap->len) {
 187         case 0:
 188                 return NULL;
 189         case 1:
 190                 (void) heap_set_len(heap, 0);
 191                 return heap->ptrs[0];
 192         }
 193         /* Shrink, replace the current max by previous last entry and heapify */
 194         heap_set_len(heap, heap->len - 1);
 195         /* len changed. previous last entry is at heap->len */
 196         return bt_heap_replace_max(heap, heap->ptrs[heap->len]);
 197 }
 198
 199 void *bt_heap_cherrypick(struct ptr_heap *heap, void *p)
 200 {
 201         size_t pos, len = heap->len;
 202
 203         for (pos = 0; pos < len; pos++)
 204                 if (unlikely(heap->ptrs[pos] == p))
 205                         goto found;
 206         return NULL;
 207 found:
 208         if (unlikely(heap->len == 1)) {
 209                 (void) heap_set_len(heap, 0);
 210                 check_heap(heap);
 211                 return heap->ptrs[0];
 212         }
 213         /* Replace p with previous last entry and heapify. */
 214         heap_set_len(heap, heap->len - 1);
 215         /* len changed. previous last entry is at heap->len */
 216         heap->ptrs[pos] = heap->ptrs[heap->len];
 217         heapify(heap, pos);
 218         return p;
 219 }
 220
 221 int bt_heap_copy(struct ptr_heap *dst, struct ptr_heap *src)
 222 {
 223         int ret;
 224
 225         ret = bt_heap_init(dst, src->alloc_len, src->gt);
 226         if (ret < 0)
 227                 goto end;
 228
 229         ret = heap_set_len(dst, src->len);
 230         if (ret < 0)
 231                 goto end;
 232
 233         memcpy(dst->ptrs, src->ptrs, src->len * sizeof(void *));
 234
 235 end:
 236         return ret;
 237 }