1 /*
2  * pairingheap.h
3  *
4  * A Pairing Heap implementation
5  *
6  * Portions Copyright (c) 2012-2021, PostgreSQL Global Development Group
7  *
8  * src/include/lib/pairingheap.h
9  */
10 
11 #ifndef PAIRINGHEAP_H
12 #define PAIRINGHEAP_H
13 
14 #include "lib/stringinfo.h"
15 
16 /* Enable if you need the pairingheap_dump() debug function */
17 /* #define PAIRINGHEAP_DEBUG */
18 
19 /*
20  * This represents an element stored in the heap. Embed this in a larger
21  * struct containing the actual data you're storing.
22  *
23  * A node can have multiple children, which form a double-linked list.
24  * first_child points to the node's first child, and the subsequent children
25  * can be found by following the next_sibling pointers. The last child has
26  * next_sibling == NULL. The prev_or_parent pointer points to the node's
27  * previous sibling, or if the node is its parent's first child, to the
28  * parent.
29  */
30 typedef struct pairingheap_node
31 {
32 	struct pairingheap_node *first_child;
33 	struct pairingheap_node *next_sibling;
34 	struct pairingheap_node *prev_or_parent;
35 } pairingheap_node;
36 
37 /*
38  * Return the containing struct of 'type' where 'membername' is the
39  * pairingheap_node pointed at by 'ptr'.
40  *
41  * This is used to convert a pairingheap_node * back to its containing struct.
42  */
43 #define pairingheap_container(type, membername, ptr) \
44 	(AssertVariableIsOfTypeMacro(ptr, pairingheap_node *), \
45 	 AssertVariableIsOfTypeMacro(((type *) NULL)->membername, pairingheap_node),  \
46 	 ((type *) ((char *) (ptr) - offsetof(type, membername))))
47 
48 /*
49  * Like pairingheap_container, but used when the pointer is 'const ptr'
50  */
51 #define pairingheap_const_container(type, membername, ptr) \
52 	(AssertVariableIsOfTypeMacro(ptr, const pairingheap_node *), \
53 	 AssertVariableIsOfTypeMacro(((type *) NULL)->membername, pairingheap_node),  \
54 	 ((const type *) ((const char *) (ptr) - offsetof(type, membername))))
55 
56 /*
57  * For a max-heap, the comparator must return <0 iff a < b, 0 iff a == b,
58  * and >0 iff a > b.  For a min-heap, the conditions are reversed.
59  */
60 typedef int (*pairingheap_comparator) (const pairingheap_node *a,
61 									   const pairingheap_node *b,
62 									   void *arg);
63 
64 /*
65  * A pairing heap.
66  *
67  * You can use pairingheap_allocate() to create a new palloc'd heap, or embed
68  * this in a larger struct, set ph_compare and ph_arg directly and initialize
69  * ph_root to NULL.
70  */
71 typedef struct pairingheap
72 {
73 	pairingheap_comparator ph_compare;	/* comparison function */
74 	void	   *ph_arg;			/* opaque argument to ph_compare */
75 	pairingheap_node *ph_root;	/* current root of the heap */
76 } pairingheap;
77 
78 extern pairingheap *pairingheap_allocate(pairingheap_comparator compare,
79 										 void *arg);
80 extern void pairingheap_free(pairingheap *heap);
81 extern void pairingheap_add(pairingheap *heap, pairingheap_node *node);
82 extern pairingheap_node *pairingheap_first(pairingheap *heap);
83 extern pairingheap_node *pairingheap_remove_first(pairingheap *heap);
84 extern void pairingheap_remove(pairingheap *heap, pairingheap_node *node);
85 
86 #ifdef PAIRINGHEAP_DEBUG
87 extern char *pairingheap_dump(pairingheap *heap,
88 							  void (*dumpfunc) (pairingheap_node *node, StringInfo buf, void *opaque),
89 							  void *opaque);
90 #endif
91 
92 /* Resets the heap to be empty. */
93 #define pairingheap_reset(h)			((h)->ph_root = NULL)
94 
95 /* Is the heap empty? */
96 #define pairingheap_is_empty(h)			((h)->ph_root == NULL)
97 
98 /* Is there exactly one node in the heap? */
99 #define pairingheap_is_singular(h) \
100 	((h)->ph_root && (h)->ph_root->first_child == NULL)
101 
102 #endif							/* PAIRINGHEAP_H */
103