1 files changed, 236 insertions, 0 deletions
diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
new file mode 100644
index 00000000..43a7b9dc
--- /dev/null
+++ b/include/linux/min_heap.h
@@ -0,0 +1,236 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MIN_HEAP_H
+#define _LINUX_MIN_HEAP_H
+
+#include <linux/bug.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+/**
+ * Data structure to hold a min-heap.
+ * @nr: Number of elements currently in the heap.
+ * @size: Maximum number of elements that can be held in current storage.
+ * @data: Pointer to the start of array holding the heap elements.
+ * @preallocated: Start of the static preallocated array holding the heap elements.
+ */
+#define MIN_HEAP_PREALLOCATED(_type, _name, _nr)	\
+struct _name {	\
+	int nr;	\
+	int size;	\
+	_type *data;	\
+	_type preallocated[_nr];	\
+}
+
+#define DEFINE_MIN_HEAP(_type, _name) MIN_HEAP_PREALLOCATED(_type, _name, 0)
+
+typedef DEFINE_MIN_HEAP(char, min_heap_char) min_heap_char;
+
+#define __minheap_cast(_heap)		(typeof((_heap)->data[0]) *)
+#define __minheap_obj_size(_heap)	sizeof((_heap)->data[0])
+
+/**
+ * struct min_heap_callbacks - Data/functions to customise the min_heap.
+ * @less: Partial order function for this heap.
+ * @swp: Swap elements function.
+ */
+struct min_heap_callbacks {
+	bool (*less)(const void *lhs, const void *rhs, void *args);
+	void (*swp)(void *lhs, void *rhs, void *args);
+};
+
+/* Initialize a min-heap. */
+static __always_inline
+void __min_heap_init(min_heap_char *heap, void *data, int size)
+{
+	heap->nr = 0;
+	heap->size = size;
+	if (data)
+		heap->data = data;
+	else
+		heap->data = heap->preallocated;
+}
+
+#define min_heap_init(_heap, _data, _size)	\
+	__min_heap_init((min_heap_char *)_heap, _data, _size)
+
+/* Get the minimum element from the heap. */
+static __always_inline
+void *__min_heap_peek(struct min_heap_char *heap)
+{
+	return heap->nr ? heap->data : NULL;
+}
+
+#define min_heap_peek(_heap)	\
+	(__minheap_cast(_heap) __min_heap_peek((min_heap_char *)_heap))
+
+/* Check if the heap is full. */
+static __always_inline
+bool __min_heap_full(min_heap_char *heap)
+{
+	return heap->nr == heap->size;
+}
+
+#define min_heap_full(_heap)	\
+	__min_heap_full((min_heap_char *)_heap)
+
+/* Sift the element at pos down the heap. */
+static __always_inline
+void __min_heap_sift_down(min_heap_char *heap, int pos, size_t elem_size,
+		const struct min_heap_callbacks *func, void *args)
+{
+	void *left, *right;
+	void *data = heap->data;
+	void *root = data + pos * elem_size;
+	int i = pos, j;
+
+	/* Find the sift-down path all the way to the leaves. */
+	for (;;) {
+		if (i * 2 + 2 >= heap->nr)
+			break;
+		left = data + (i * 2 + 1) * elem_size;
+		right = data + (i * 2 + 2) * elem_size;
+		i = func->less(left, right, args) ? i * 2 + 1 : i * 2 + 2;
+	}
+
+	/* Special case for the last leaf with no sibling. */
+	if (i * 2 + 2 == heap->nr)
+		i = i * 2 + 1;
+
+	/* Backtrack to the correct location. */
+	while (i != pos && func->less(root, data + i * elem_size, args))
+		i = (i - 1) / 2;
+
+	/* Shift the element into its correct place. */
+	j = i;
+	while (i != pos) {
+		i = (i - 1) / 2;
+		func->swp(data + i * elem_size, data + j * elem_size, args);
+	}
+}
+
+#define min_heap_sift_down(_heap, _pos, _func, _args)	\
+	__min_heap_sift_down((min_heap_char *)_heap, _pos, __minheap_obj_size(_heap), _func, _args)
+
+/* Sift up ith element from the heap, O(log2(nr)). */
+static __always_inline
+void __min_heap_sift_up(min_heap_char *heap, size_t elem_size, size_t idx,
+		const struct min_heap_callbacks *func, void *args)
+{
+	void *data = heap->data;
+	size_t parent;
+
+	while (idx) {
+		parent = (idx - 1) / 2;
+		if (func->less(data + parent * elem_size, data + idx * elem_size, args))
+			break;
+		func->swp(data + parent * elem_size, data + idx * elem_size, args);
+		idx = parent;
+	}
+}
+
+#define min_heap_sift_up(_heap, _idx, _func, _args)	\
+	__min_heap_sift_up((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx, _func, _args)
+
+/* Floyd's approach to heapification that is O(nr). */
+static __always_inline
+void __min_heapify_all(min_heap_char *heap, size_t elem_size,
+		const struct min_heap_callbacks *func, void *args)
+{
+	int i;
+
+	for (i = heap->nr / 2 - 1; i >= 0; i--)
+		__min_heap_sift_down(heap, i, elem_size, func, args);
+}
+
+#define min_heapify_all(_heap, _func, _args)	\
+	__min_heapify_all((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+
+/* Remove minimum element from the heap, O(log2(nr)). */
+static __always_inline
+bool __min_heap_pop(min_heap_char *heap, size_t elem_size,
+		const struct min_heap_callbacks *func, void *args)
+{
+	void *data = heap->data;
+
+	if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
+		return false;
+
+	/* Place last element at the root (position 0) and then sift down. */
+	heap->nr--;
+	memcpy(data, data + (heap->nr * elem_size), elem_size);
+	__min_heap_sift_down(heap, 0, elem_size, func, args);
+
+	return true;
+}
+
+#define min_heap_pop(_heap, _func, _args)	\
+	__min_heap_pop((min_heap_char *)_heap, __minheap_obj_size(_heap), _func, _args)
+
+/*
+ * Remove the minimum element and then push the given element. The
+ * implementation performs 1 sift (O(log2(nr))) and is therefore more
+ * efficient than a pop followed by a push that does 2.
+ */
+static __always_inline
+void __min_heap_pop_push(min_heap_char *heap,
+		const void *element, size_t elem_size,
+		const struct min_heap_callbacks *func,
+		void *args)
+{
+	memcpy(heap->data, element, elem_size);
+	__min_heap_sift_down(heap, 0, elem_size, func, args);
+}
+
+#define min_heap_pop_push(_heap, _element, _func, _args)	\
+	__min_heap_pop_push((min_heap_char *)_heap, _element, __minheap_obj_size(_heap), _func, _args)
+
+/* Push an element on to the heap, O(log2(nr)). */
+static __always_inline
+bool __min_heap_push(min_heap_char *heap, const void *element, size_t elem_size,
+		const struct min_heap_callbacks *func, void *args)
+{
+	void *data = heap->data;
+	int pos;
+
+	if (WARN_ONCE(heap->nr >= heap->size, "Pushing on a full heap"))
+		return false;
+
+	/* Place at the end of data. */
+	pos = heap->nr;
+	memcpy(data + (pos * elem_size), element, elem_size);
+	heap->nr++;
+
+	/* Sift child at pos up. */
+	__min_heap_sift_up(heap, elem_size, pos, func, args);
+
+	return true;
+}
+
+#define min_heap_push(_heap, _element, _func, _args)	\
+	__min_heap_push((min_heap_char *)_heap, _element, __minheap_obj_size(_heap), _func, _args)
+
+/* Remove ith element from the heap, O(log2(nr)). */
+static __always_inline
+bool __min_heap_del(min_heap_char *heap, size_t elem_size, size_t idx,
+		const struct min_heap_callbacks *func, void *args)
+{
+	void *data = heap->data;
+
+	if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
+		return false;
+
+	/* Place last element at the root (position 0) and then sift down. */
+	heap->nr--;
+	if (idx == heap->nr)
+		return true;
+	func->swp(data + (idx * elem_size), data + (heap->nr * elem_size), args);
+	__min_heap_sift_up(heap, elem_size, idx, func, args);
+	__min_heap_sift_down(heap, idx, elem_size, func, args);
+
+	return true;
+}
+
+#define min_heap_del(_heap, _idx, _func, _args)	\
+	__min_heap_del((min_heap_char *)_heap, __minheap_obj_size(_heap), _idx, _func, _args)
+
+#endif /* _LINUX_MIN_HEAP_H */