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6e24628d78
Supports push, pop and converting an array into a heap. If the sense of the compare function is inverted then it can provide a max-heap. Based-on-work-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ian Rogers <irogers@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20200214075133.181299-3-irogers@google.com
135 lines
3.3 KiB
C
135 lines
3.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_MIN_HEAP_H
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#define _LINUX_MIN_HEAP_H
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#include <linux/bug.h>
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#include <linux/string.h>
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#include <linux/types.h>
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/**
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* struct min_heap - Data structure to hold a min-heap.
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* @data: Start of array holding the heap elements.
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* @nr: Number of elements currently in the heap.
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* @size: Maximum number of elements that can be held in current storage.
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*/
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struct min_heap {
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void *data;
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int nr;
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int size;
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};
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/**
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* struct min_heap_callbacks - Data/functions to customise the min_heap.
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* @elem_size: The nr of each element in bytes.
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* @less: Partial order function for this heap.
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* @swp: Swap elements function.
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*/
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struct min_heap_callbacks {
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int elem_size;
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bool (*less)(const void *lhs, const void *rhs);
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void (*swp)(void *lhs, void *rhs);
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};
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/* Sift the element at pos down the heap. */
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static __always_inline
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void min_heapify(struct min_heap *heap, int pos,
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const struct min_heap_callbacks *func)
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{
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void *left, *right, *parent, *smallest;
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void *data = heap->data;
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for (;;) {
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if (pos * 2 + 1 >= heap->nr)
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break;
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left = data + ((pos * 2 + 1) * func->elem_size);
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parent = data + (pos * func->elem_size);
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smallest = parent;
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if (func->less(left, smallest))
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smallest = left;
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if (pos * 2 + 2 < heap->nr) {
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right = data + ((pos * 2 + 2) * func->elem_size);
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if (func->less(right, smallest))
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smallest = right;
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}
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if (smallest == parent)
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break;
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func->swp(smallest, parent);
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if (smallest == left)
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pos = (pos * 2) + 1;
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else
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pos = (pos * 2) + 2;
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}
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}
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/* Floyd's approach to heapification that is O(nr). */
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static __always_inline
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void min_heapify_all(struct min_heap *heap,
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const struct min_heap_callbacks *func)
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{
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int i;
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for (i = heap->nr / 2; i >= 0; i--)
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min_heapify(heap, i, func);
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}
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/* Remove minimum element from the heap, O(log2(nr)). */
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static __always_inline
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void min_heap_pop(struct min_heap *heap,
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const struct min_heap_callbacks *func)
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{
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void *data = heap->data;
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if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
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return;
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/* Place last element at the root (position 0) and then sift down. */
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heap->nr--;
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memcpy(data, data + (heap->nr * func->elem_size), func->elem_size);
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min_heapify(heap, 0, func);
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}
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/*
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* Remove the minimum element and then push the given element. The
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* implementation performs 1 sift (O(log2(nr))) and is therefore more
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* efficient than a pop followed by a push that does 2.
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*/
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static __always_inline
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void min_heap_pop_push(struct min_heap *heap,
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const void *element,
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const struct min_heap_callbacks *func)
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{
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memcpy(heap->data, element, func->elem_size);
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min_heapify(heap, 0, func);
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}
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/* Push an element on to the heap, O(log2(nr)). */
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static __always_inline
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void min_heap_push(struct min_heap *heap, const void *element,
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const struct min_heap_callbacks *func)
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{
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void *data = heap->data;
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void *child, *parent;
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int pos;
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if (WARN_ONCE(heap->nr >= heap->size, "Pushing on a full heap"))
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return;
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/* Place at the end of data. */
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pos = heap->nr;
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memcpy(data + (pos * func->elem_size), element, func->elem_size);
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heap->nr++;
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/* Sift child at pos up. */
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for (; pos > 0; pos = (pos - 1) / 2) {
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child = data + (pos * func->elem_size);
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parent = data + ((pos - 1) / 2) * func->elem_size;
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if (func->less(parent, child))
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break;
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func->swp(parent, child);
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}
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}
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#endif /* _LINUX_MIN_HEAP_H */
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