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author | Nathan Bossart <nathan@postgresql.org> | 2023-09-18 12:18:33 -0700 |
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committer | Nathan Bossart <nathan@postgresql.org> | 2023-09-18 12:18:33 -0700 |
commit | 5af0263afd7beaf947e22115b7e9ade000b0387d (patch) | |
tree | bfbf27f3bcf3de8580d24e25bdc9b4b21a687bed /src/backend/lib/binaryheap.c | |
parent | f73fa5a470b4cf850ad404b63c3e352d179d40b0 (diff) | |
download | postgresql-5af0263afd7beaf947e22115b7e9ade000b0387d.tar.gz postgresql-5af0263afd7beaf947e22115b7e9ade000b0387d.zip |
Make binaryheap available to frontend code.
There are a couple of places in frontend code that could make use
of this simple binary heap implementation. This commit makes
binaryheap usable in frontend code, much like commit 26aaf97b68 did
for StringInfo. Like StringInfo, the header file is left in lib/
to reduce the likelihood of unnecessary breakage.
The frontend version of binaryheap exposes a void *-based API since
frontend code does not have access to the Datum definitions. This
seemed like a better approach than switching all existing uses to
void * or making the Datum definitions available to frontend code.
Reviewed-by: Tom Lane, Alvaro Herrera
Discussion: https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us
Diffstat (limited to 'src/backend/lib/binaryheap.c')
-rw-r--r-- | src/backend/lib/binaryheap.c | 317 |
1 files changed, 0 insertions, 317 deletions
diff --git a/src/backend/lib/binaryheap.c b/src/backend/lib/binaryheap.c deleted file mode 100644 index 17375467578..00000000000 --- a/src/backend/lib/binaryheap.c +++ /dev/null @@ -1,317 +0,0 @@ -/*------------------------------------------------------------------------- - * - * binaryheap.c - * A simple binary heap implementation - * - * Portions Copyright (c) 2012-2023, PostgreSQL Global Development Group - * - * IDENTIFICATION - * src/backend/lib/binaryheap.c - * - *------------------------------------------------------------------------- - */ - -#include "postgres.h" - -#include <math.h> - -#include "lib/binaryheap.h" - -static void sift_down(binaryheap *heap, int node_off); -static void sift_up(binaryheap *heap, int node_off); - -/* - * binaryheap_allocate - * - * Returns a pointer to a newly-allocated heap that has the capacity to - * store the given number of nodes, with the heap property defined by - * the given comparator function, which will be invoked with the additional - * argument specified by 'arg'. - */ -binaryheap * -binaryheap_allocate(int capacity, binaryheap_comparator compare, void *arg) -{ - int sz; - binaryheap *heap; - - sz = offsetof(binaryheap, bh_nodes) + sizeof(Datum) * capacity; - heap = (binaryheap *) palloc(sz); - heap->bh_space = capacity; - heap->bh_compare = compare; - heap->bh_arg = arg; - - heap->bh_size = 0; - heap->bh_has_heap_property = true; - - return heap; -} - -/* - * binaryheap_reset - * - * Resets the heap to an empty state, losing its data content but not the - * parameters passed at allocation. - */ -void -binaryheap_reset(binaryheap *heap) -{ - heap->bh_size = 0; - heap->bh_has_heap_property = true; -} - -/* - * binaryheap_free - * - * Releases memory used by the given binaryheap. - */ -void -binaryheap_free(binaryheap *heap) -{ - pfree(heap); -} - -/* - * These utility functions return the offset of the left child, right - * child, and parent of the node at the given index, respectively. - * - * The heap is represented as an array of nodes, with the root node - * stored at index 0. The left child of node i is at index 2*i+1, and - * the right child at 2*i+2. The parent of node i is at index (i-1)/2. - */ - -static inline int -left_offset(int i) -{ - return 2 * i + 1; -} - -static inline int -right_offset(int i) -{ - return 2 * i + 2; -} - -static inline int -parent_offset(int i) -{ - return (i - 1) / 2; -} - -/* - * binaryheap_add_unordered - * - * Adds the given datum to the end of the heap's list of nodes in O(1) without - * preserving the heap property. This is a convenience to add elements quickly - * to a new heap. To obtain a valid heap, one must call binaryheap_build() - * afterwards. - */ -void -binaryheap_add_unordered(binaryheap *heap, Datum d) -{ - if (heap->bh_size >= heap->bh_space) - elog(ERROR, "out of binary heap slots"); - heap->bh_has_heap_property = false; - heap->bh_nodes[heap->bh_size] = d; - heap->bh_size++; -} - -/* - * binaryheap_build - * - * Assembles a valid heap in O(n) from the nodes added by - * binaryheap_add_unordered(). Not needed otherwise. - */ -void -binaryheap_build(binaryheap *heap) -{ - int i; - - for (i = parent_offset(heap->bh_size - 1); i >= 0; i--) - sift_down(heap, i); - heap->bh_has_heap_property = true; -} - -/* - * binaryheap_add - * - * Adds the given datum to the heap in O(log n) time, while preserving - * the heap property. - */ -void -binaryheap_add(binaryheap *heap, Datum d) -{ - if (heap->bh_size >= heap->bh_space) - elog(ERROR, "out of binary heap slots"); - heap->bh_nodes[heap->bh_size] = d; - heap->bh_size++; - sift_up(heap, heap->bh_size - 1); -} - -/* - * binaryheap_first - * - * Returns a pointer to the first (root, topmost) node in the heap - * without modifying the heap. The caller must ensure that this - * routine is not used on an empty heap. Always O(1). - */ -Datum -binaryheap_first(binaryheap *heap) -{ - Assert(!binaryheap_empty(heap) && heap->bh_has_heap_property); - return heap->bh_nodes[0]; -} - -/* - * binaryheap_remove_first - * - * Removes the first (root, topmost) node in the heap and returns a - * pointer to it after rebalancing the heap. The caller must ensure - * that this routine is not used on an empty heap. O(log n) worst - * case. - */ -Datum -binaryheap_remove_first(binaryheap *heap) -{ - Datum result; - - Assert(!binaryheap_empty(heap) && heap->bh_has_heap_property); - - /* extract the root node, which will be the result */ - result = heap->bh_nodes[0]; - - /* easy if heap contains one element */ - if (heap->bh_size == 1) - { - heap->bh_size--; - return result; - } - - /* - * Remove the last node, placing it in the vacated root entry, and sift - * the new root node down to its correct position. - */ - heap->bh_nodes[0] = heap->bh_nodes[--heap->bh_size]; - sift_down(heap, 0); - - return result; -} - -/* - * binaryheap_replace_first - * - * Replace the topmost element of a non-empty heap, preserving the heap - * property. O(1) in the best case, or O(log n) if it must fall back to - * sifting the new node down. - */ -void -binaryheap_replace_first(binaryheap *heap, Datum d) -{ - Assert(!binaryheap_empty(heap) && heap->bh_has_heap_property); - - heap->bh_nodes[0] = d; - - if (heap->bh_size > 1) - sift_down(heap, 0); -} - -/* - * Sift a node up to the highest position it can hold according to the - * comparator. - */ -static void -sift_up(binaryheap *heap, int node_off) -{ - Datum node_val = heap->bh_nodes[node_off]; - - /* - * Within the loop, the node_off'th array entry is a "hole" that - * notionally holds node_val, but we don't actually store node_val there - * till the end, saving some unnecessary data copying steps. - */ - while (node_off != 0) - { - int cmp; - int parent_off; - Datum parent_val; - - /* - * If this node is smaller than its parent, the heap condition is - * satisfied, and we're done. - */ - parent_off = parent_offset(node_off); - parent_val = heap->bh_nodes[parent_off]; - cmp = heap->bh_compare(node_val, - parent_val, - heap->bh_arg); - if (cmp <= 0) - break; - - /* - * Otherwise, swap the parent value with the hole, and go on to check - * the node's new parent. - */ - heap->bh_nodes[node_off] = parent_val; - node_off = parent_off; - } - /* Re-fill the hole */ - heap->bh_nodes[node_off] = node_val; -} - -/* - * Sift a node down from its current position to satisfy the heap - * property. - */ -static void -sift_down(binaryheap *heap, int node_off) -{ - Datum node_val = heap->bh_nodes[node_off]; - - /* - * Within the loop, the node_off'th array entry is a "hole" that - * notionally holds node_val, but we don't actually store node_val there - * till the end, saving some unnecessary data copying steps. - */ - while (true) - { - int left_off = left_offset(node_off); - int right_off = right_offset(node_off); - int swap_off = 0; - - /* Is the left child larger than the parent? */ - if (left_off < heap->bh_size && - heap->bh_compare(node_val, - heap->bh_nodes[left_off], - heap->bh_arg) < 0) - swap_off = left_off; - - /* Is the right child larger than the parent? */ - if (right_off < heap->bh_size && - heap->bh_compare(node_val, - heap->bh_nodes[right_off], - heap->bh_arg) < 0) - { - /* swap with the larger child */ - if (!swap_off || - heap->bh_compare(heap->bh_nodes[left_off], - heap->bh_nodes[right_off], - heap->bh_arg) < 0) - swap_off = right_off; - } - - /* - * If we didn't find anything to swap, the heap condition is - * satisfied, and we're done. - */ - if (!swap_off) - break; - - /* - * Otherwise, swap the hole with the child that violates the heap - * property; then go on to check its children. - */ - heap->bh_nodes[node_off] = heap->bh_nodes[swap_off]; - node_off = swap_off; - } - /* Re-fill the hole */ - heap->bh_nodes[node_off] = node_val; -} |