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f3bc08c5 | 1 | /* |
162769ef MD |
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. | |
f3bc08c5 MD |
18 | */ |
19 | ||
20 | #include <linux/slab.h> | |
21 | #include <linux/prio_heap.h> | |
22 | ||
162769ef MD |
23 | /* |
24 | * TODO implement heap_init, heap_free, heap_insert. | |
25 | */ | |
f3bc08c5 MD |
26 | |
27 | static void heapify(struct ptr_heap *heap, int pos) | |
28 | { | |
29 | void **ptrs = heap->ptrs; | |
30 | void *p = ptrs[pos]; | |
31 | ||
32 | while (1) { | |
33 | int left = 2 * pos + 1; | |
34 | int right = 2 * pos + 2; | |
35 | int largest = pos; | |
36 | if (left < heap->size && heap->gt(ptrs[left], p)) | |
37 | largest = left; | |
38 | if (right < heap->size && heap->gt(ptrs[right], ptrs[largest])) | |
39 | largest = right; | |
40 | if (largest == pos) | |
41 | break; | |
42 | /* Push p down the heap one level and bump one up */ | |
43 | ptrs[pos] = ptrs[largest]; | |
44 | ptrs[largest] = p; | |
45 | pos = largest; | |
46 | } | |
47 | } | |
48 | ||
49 | void *heap_replace_max(struct ptr_heap *heap, void *p) | |
50 | { | |
51 | void *res; | |
52 | void **ptrs = heap->ptrs; | |
53 | ||
54 | if (!heap->size) { | |
55 | ptrs[0] = p; | |
56 | heap->size = 1; | |
57 | return NULL; | |
58 | } | |
59 | ||
60 | /* Replace the current max and heapify */ | |
61 | res = ptrs[0]; | |
62 | ptrs[0] = p; | |
63 | heapify(heap, 0); | |
64 | return res; | |
65 | } | |
66 | ||
f3bc08c5 MD |
67 | void *heap_remove(struct ptr_heap *heap) |
68 | { | |
69 | void **ptrs = heap->ptrs; | |
70 | ||
71 | switch (heap->size) { | |
72 | case 0: | |
73 | return NULL; | |
74 | case 1: | |
75 | heap->size = 0; | |
76 | return ptrs[0]; | |
77 | } | |
78 | ||
79 | /* Shrink, replace the current max by previous last entry and heapify */ | |
80 | return heap_replace_max(heap, ptrs[--heap->size]); | |
81 | } | |
82 | ||
83 | void *heap_cherrypick(struct ptr_heap *heap, void *p) | |
84 | { | |
85 | void **ptrs = heap->ptrs; | |
86 | size_t pos, size = heap->size; | |
87 | ||
88 | for (pos = 0; pos < size; pos++) | |
89 | if (ptrs[pos] == p) | |
90 | goto found; | |
91 | return NULL; | |
92 | found: | |
93 | if (heap->size == 1) { | |
94 | heap->size = 0; | |
95 | return ptrs[0]; | |
96 | } | |
97 | /* | |
98 | * Replace p with previous last entry and heapify. | |
99 | */ | |
100 | ptrs[pos] = ptrs[--heap->size]; | |
101 | heapify(heap, pos); | |
102 | return p; | |
103 | } |