1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_MIN_HEAP_H
3 #define _LINUX_MIN_HEAP_H
4
5 #include <linux/bug.h>
6 #include <linux/string.h>
7 #include <linux/types.h>
8
9 /**
10 * struct min_heap - Data structure to hold a min-heap.
11 * @data: Start of array holding the heap elements.
12 * @nr: Number of elements currently in the heap.
13 * @size: Maximum number of elements that can be held in current storage.
14 */
15 struct min_heap {
16 void *data;
17 int nr;
18 int size;
19 };
20
21 /**
22 * struct min_heap_callbacks - Data/functions to customise the min_heap.
23 * @elem_size: The nr of each element in bytes.
24 * @less: Partial order function for this heap.
25 * @swp: Swap elements function.
26 */
27 struct min_heap_callbacks {
28 int elem_size;
29 bool (*less)(const void *lhs, const void *rhs);
30 void (*swp)(void *lhs, void *rhs);
31 };
32
33 /* Sift the element at pos down the heap. */
34 static __always_inline
min_heapify(struct min_heap * heap,int pos,const struct min_heap_callbacks * func)35 void min_heapify(struct min_heap *heap, int pos,
36 const struct min_heap_callbacks *func)
37 {
38 void *left, *right, *parent, *smallest;
39 void *data = heap->data;
40
41 for (;;) {
42 if (pos * 2 + 1 >= heap->nr)
43 break;
44
45 left = data + ((pos * 2 + 1) * func->elem_size);
46 parent = data + (pos * func->elem_size);
47 smallest = parent;
48 if (func->less(left, smallest))
49 smallest = left;
50
51 if (pos * 2 + 2 < heap->nr) {
52 right = data + ((pos * 2 + 2) * func->elem_size);
53 if (func->less(right, smallest))
54 smallest = right;
55 }
56 if (smallest == parent)
57 break;
58 func->swp(smallest, parent);
59 if (smallest == left)
60 pos = (pos * 2) + 1;
61 else
62 pos = (pos * 2) + 2;
63 }
64 }
65
66 /* Floyd's approach to heapification that is O(nr). */
67 static __always_inline
min_heapify_all(struct min_heap * heap,const struct min_heap_callbacks * func)68 void min_heapify_all(struct min_heap *heap,
69 const struct min_heap_callbacks *func)
70 {
71 int i;
72
73 for (i = heap->nr / 2; i >= 0; i--)
74 min_heapify(heap, i, func);
75 }
76
77 /* Remove minimum element from the heap, O(log2(nr)). */
78 static __always_inline
min_heap_pop(struct min_heap * heap,const struct min_heap_callbacks * func)79 void min_heap_pop(struct min_heap *heap,
80 const struct min_heap_callbacks *func)
81 {
82 void *data = heap->data;
83
84 if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
85 return;
86
87 /* Place last element at the root (position 0) and then sift down. */
88 heap->nr--;
89 memcpy(data, data + (heap->nr * func->elem_size), func->elem_size);
90 min_heapify(heap, 0, func);
91 }
92
93 /*
94 * Remove the minimum element and then push the given element. The
95 * implementation performs 1 sift (O(log2(nr))) and is therefore more
96 * efficient than a pop followed by a push that does 2.
97 */
98 static __always_inline
min_heap_pop_push(struct min_heap * heap,const void * element,const struct min_heap_callbacks * func)99 void min_heap_pop_push(struct min_heap *heap,
100 const void *element,
101 const struct min_heap_callbacks *func)
102 {
103 memcpy(heap->data, element, func->elem_size);
104 min_heapify(heap, 0, func);
105 }
106
107 /* Push an element on to the heap, O(log2(nr)). */
108 static __always_inline
min_heap_push(struct min_heap * heap,const void * element,const struct min_heap_callbacks * func)109 void min_heap_push(struct min_heap *heap, const void *element,
110 const struct min_heap_callbacks *func)
111 {
112 void *data = heap->data;
113 void *child, *parent;
114 int pos;
115
116 if (WARN_ONCE(heap->nr >= heap->size, "Pushing on a full heap"))
117 return;
118
119 /* Place at the end of data. */
120 pos = heap->nr;
121 memcpy(data + (pos * func->elem_size), element, func->elem_size);
122 heap->nr++;
123
124 /* Sift child at pos up. */
125 for (; pos > 0; pos = (pos - 1) / 2) {
126 child = data + (pos * func->elem_size);
127 parent = data + ((pos - 1) / 2) * func->elem_size;
128 if (func->less(parent, child))
129 break;
130 func->swp(parent, child);
131 }
132 }
133
134 #endif /* _LINUX_MIN_HEAP_H */
135