lib: Introduce generic min-heap
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
This commit is contained in:
Ian Rogers
Ingo Molnar
parent
98add2af89
commit
6e24628d78
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@ -0,0 +1,134 @@
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/* 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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@ -1769,6 +1769,16 @@ config TEST_LIST_SORT
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If unsure, say N.
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config TEST_MIN_HEAP
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tristate "Min heap test"
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depends on DEBUG_KERNEL || m
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help
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Enable this to turn on min heap function tests. This test is
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executed only once during system boot (so affects only boot time),
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or at module load time.
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If unsure, say N.
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config TEST_SORT
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tristate "Array-based sort test"
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depends on DEBUG_KERNEL || m
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@ -67,6 +67,7 @@ CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
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UBSAN_SANITIZE_test_ubsan.o := y
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obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
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obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
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obj-$(CONFIG_TEST_MIN_HEAP) += test_min_heap.o
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obj-$(CONFIG_TEST_LKM) += test_module.o
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obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
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obj-$(CONFIG_TEST_OVERFLOW) += test_overflow.o
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@ -0,0 +1,194 @@
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// SPDX-License-Identifier: GPL-2.0-only
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#define pr_fmt(fmt) "min_heap_test: " fmt
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/*
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* Test cases for the min max heap.
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*/
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#include <linux/log2.h>
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#include <linux/min_heap.h>
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#include <linux/module.h>
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#include <linux/printk.h>
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#include <linux/random.h>
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static __init bool less_than(const void *lhs, const void *rhs)
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{
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return *(int *)lhs < *(int *)rhs;
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}
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static __init bool greater_than(const void *lhs, const void *rhs)
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{
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return *(int *)lhs > *(int *)rhs;
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}
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static __init void swap_ints(void *lhs, void *rhs)
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{
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int temp = *(int *)lhs;
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*(int *)lhs = *(int *)rhs;
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*(int *)rhs = temp;
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}
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static __init int pop_verify_heap(bool min_heap,
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struct min_heap *heap,
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const struct min_heap_callbacks *funcs)
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{
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int *values = heap->data;
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int err = 0;
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int last;
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last = values[0];
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min_heap_pop(heap, funcs);
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while (heap->nr > 0) {
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if (min_heap) {
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if (last > values[0]) {
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pr_err("error: expected %d <= %d\n", last,
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values[0]);
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err++;
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}
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} else {
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if (last < values[0]) {
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pr_err("error: expected %d >= %d\n", last,
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values[0]);
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err++;
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}
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}
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last = values[0];
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min_heap_pop(heap, funcs);
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}
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return err;
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}
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static __init int test_heapify_all(bool min_heap)
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{
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int values[] = { 3, 1, 2, 4, 0x8000000, 0x7FFFFFF, 0,
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-3, -1, -2, -4, 0x8000000, 0x7FFFFFF };
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struct min_heap heap = {
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.data = values,
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.nr = ARRAY_SIZE(values),
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.size = ARRAY_SIZE(values),
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};
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struct min_heap_callbacks funcs = {
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.elem_size = sizeof(int),
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.less = min_heap ? less_than : greater_than,
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.swp = swap_ints,
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};
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int i, err;
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/* Test with known set of values. */
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min_heapify_all(&heap, &funcs);
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err = pop_verify_heap(min_heap, &heap, &funcs);
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/* Test with randomly generated values. */
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heap.nr = ARRAY_SIZE(values);
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for (i = 0; i < heap.nr; i++)
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values[i] = get_random_int();
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min_heapify_all(&heap, &funcs);
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err += pop_verify_heap(min_heap, &heap, &funcs);
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return err;
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}
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static __init int test_heap_push(bool min_heap)
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{
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const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
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-3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
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int values[ARRAY_SIZE(data)];
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struct min_heap heap = {
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.data = values,
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.nr = 0,
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.size = ARRAY_SIZE(values),
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};
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struct min_heap_callbacks funcs = {
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.elem_size = sizeof(int),
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.less = min_heap ? less_than : greater_than,
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.swp = swap_ints,
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};
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int i, temp, err;
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/* Test with known set of values copied from data. */
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for (i = 0; i < ARRAY_SIZE(data); i++)
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min_heap_push(&heap, &data[i], &funcs);
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err = pop_verify_heap(min_heap, &heap, &funcs);
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/* Test with randomly generated values. */
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while (heap.nr < heap.size) {
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temp = get_random_int();
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min_heap_push(&heap, &temp, &funcs);
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}
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err += pop_verify_heap(min_heap, &heap, &funcs);
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return err;
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}
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static __init int test_heap_pop_push(bool min_heap)
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{
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const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
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-3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
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int values[ARRAY_SIZE(data)];
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struct min_heap heap = {
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.data = values,
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.nr = 0,
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.size = ARRAY_SIZE(values),
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};
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struct min_heap_callbacks funcs = {
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.elem_size = sizeof(int),
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.less = min_heap ? less_than : greater_than,
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.swp = swap_ints,
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};
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int i, temp, err;
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/* Fill values with data to pop and replace. */
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temp = min_heap ? 0x80000000 : 0x7FFFFFFF;
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for (i = 0; i < ARRAY_SIZE(data); i++)
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min_heap_push(&heap, &temp, &funcs);
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/* Test with known set of values copied from data. */
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for (i = 0; i < ARRAY_SIZE(data); i++)
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min_heap_pop_push(&heap, &data[i], &funcs);
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err = pop_verify_heap(min_heap, &heap, &funcs);
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heap.nr = 0;
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for (i = 0; i < ARRAY_SIZE(data); i++)
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min_heap_push(&heap, &temp, &funcs);
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/* Test with randomly generated values. */
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for (i = 0; i < ARRAY_SIZE(data); i++) {
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temp = get_random_int();
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min_heap_pop_push(&heap, &temp, &funcs);
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}
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err += pop_verify_heap(min_heap, &heap, &funcs);
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return err;
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}
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static int __init test_min_heap_init(void)
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{
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int err = 0;
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err += test_heapify_all(true);
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err += test_heapify_all(false);
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err += test_heap_push(true);
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err += test_heap_push(false);
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err += test_heap_pop_push(true);
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err += test_heap_pop_push(false);
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if (err) {
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pr_err("test failed with %d errors\n", err);
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return -EINVAL;
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}
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pr_info("test passed\n");
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return 0;
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}
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module_init(test_min_heap_init);
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static void __exit test_min_heap_exit(void)
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{
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/* do nothing */
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}
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module_exit(test_min_heap_exit);
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MODULE_LICENSE("GPL");
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