1 files changed, 319 insertions, 0 deletions
diff --git a/fs/bcachefs/eytzinger.h b/fs/bcachefs/eytzinger.h
new file mode 100644
index 000000000000..0541192d7bc0
--- /dev/null
+++ b/fs/bcachefs/eytzinger.h
@@ -0,0 +1,319 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _EYTZINGER_H
+#define _EYTZINGER_H
+
+#include <linux/bitops.h>
+#include <linux/log2.h>
+
+#ifdef EYTZINGER_DEBUG
+#define EYTZINGER_BUG_ON(cond)		BUG_ON(cond)
+#else
+#define EYTZINGER_BUG_ON(cond)
+#endif
+
+/*
+ * Traversal for trees in eytzinger layout - a full binary tree layed out in an
+ * array.
+ *
+ * Consider using an eytzinger tree any time you would otherwise be doing binary
+ * search over an array. Binary search is a worst case scenario for branch
+ * prediction and prefetching, but in an eytzinger tree every node's children
+ * are adjacent in memory, thus we can prefetch children before knowing the
+ * result of the comparison, assuming multiple nodes fit on a cacheline.
+ *
+ * Two variants are provided, for one based indexing and zero based indexing.
+ *
+ * Zero based indexing is more convenient, but one based indexing has better
+ * alignment and thus better performance because each new level of the tree
+ * starts at a power of two, and thus if element 0 was cacheline aligned, each
+ * new level will be as well.
+ */
+
+static inline unsigned eytzinger1_child(unsigned i, unsigned child)
+{
+	EYTZINGER_BUG_ON(child > 1);
+
+	return (i << 1) + child;
+}
+
+static inline unsigned eytzinger1_left_child(unsigned i)
+{
+	return eytzinger1_child(i, 0);
+}
+
+static inline unsigned eytzinger1_right_child(unsigned i)
+{
+	return eytzinger1_child(i, 1);
+}
+
+static inline unsigned eytzinger1_first(unsigned size)
+{
+	return size ? rounddown_pow_of_two(size) : 0;
+}
+
+static inline unsigned eytzinger1_last(unsigned size)
+{
+	return rounddown_pow_of_two(size + 1) - 1;
+}
+
+/*
+ * eytzinger1_next() and eytzinger1_prev() have the nice properties that
+ *
+ * eytzinger1_next(0) == eytzinger1_first())
+ * eytzinger1_prev(0) == eytzinger1_last())
+ *
+ * eytzinger1_prev(eytzinger1_first()) == 0
+ * eytzinger1_next(eytzinger1_last()) == 0
+ */
+
+static inline unsigned eytzinger1_next(unsigned i, unsigned size)
+{
+	EYTZINGER_BUG_ON(i > size);
+
+	if (eytzinger1_right_child(i) <= size) {
+		i = eytzinger1_right_child(i);
+
+		i <<= __fls(size + 1) - __fls(i);
+		i >>= i > size;
+	} else {
+		i >>= ffz(i) + 1;
+	}
+
+	return i;
+}
+
+static inline unsigned eytzinger1_prev(unsigned i, unsigned size)
+{
+	EYTZINGER_BUG_ON(i > size);
+
+	if (eytzinger1_left_child(i) <= size) {
+		i = eytzinger1_left_child(i) + 1;
+
+		i <<= __fls(size + 1) - __fls(i);
+		i -= 1;
+		i >>= i > size;
+	} else {
+		i >>= __ffs(i) + 1;
+	}
+
+	return i;
+}
+
+static inline unsigned eytzinger1_extra(unsigned size)
+{
+	return size
+		? (size + 1 - rounddown_pow_of_two(size)) << 1
+		: 0;
+}
+
+static inline unsigned __eytzinger1_to_inorder(unsigned i, unsigned size,
+					      unsigned extra)
+{
+	unsigned b = __fls(i);
+	unsigned shift = __fls(size) - b;
+	int s;
+
+	EYTZINGER_BUG_ON(!i || i > size);
+
+	i  ^= 1U << b;
+	i <<= 1;
+	i  |= 1;
+	i <<= shift;
+
+	/*
+	 * sign bit trick:
+	 *
+	 * if (i > extra)
+	 *	i -= (i - extra) >> 1;
+	 */
+	s = extra - i;
+	i += (s >> 1) & (s >> 31);
+
+	return i;
+}
+
+static inline unsigned __inorder_to_eytzinger1(unsigned i, unsigned size,
+					       unsigned extra)
+{
+	unsigned shift;
+	int s;
+
+	EYTZINGER_BUG_ON(!i || i > size);
+
+	/*
+	 * sign bit trick:
+	 *
+	 * if (i > extra)
+	 *	i += i - extra;
+	 */
+	s = extra - i;
+	i -= s & (s >> 31);
+
+	shift = __ffs(i);
+
+	i >>= shift + 1;
+	i  |= 1U << (__fls(size) - shift);
+
+	return i;
+}
+
+static inline unsigned eytzinger1_to_inorder(unsigned i, unsigned size)
+{
+	return __eytzinger1_to_inorder(i, size, eytzinger1_extra(size));
+}
+
+static inline unsigned inorder_to_eytzinger1(unsigned i, unsigned size)
+{
+	return __inorder_to_eytzinger1(i, size, eytzinger1_extra(size));
+}
+
+#define eytzinger1_for_each(_i, _size)			\
+	for (unsigned (_i) = eytzinger1_first((_size));	\
+	     (_i) != 0;					\
+	     (_i) = eytzinger1_next((_i), (_size)))
+
+/* Zero based indexing version: */
+
+static inline unsigned eytzinger0_child(unsigned i, unsigned child)
+{
+	EYTZINGER_BUG_ON(child > 1);
+
+	return (i << 1) + 1 + child;
+}
+
+static inline unsigned eytzinger0_left_child(unsigned i)
+{
+	return eytzinger0_child(i, 0);
+}
+
+static inline unsigned eytzinger0_right_child(unsigned i)
+{
+	return eytzinger0_child(i, 1);
+}
+
+static inline unsigned eytzinger0_first(unsigned size)
+{
+	return eytzinger1_first(size) - 1;
+}
+
+static inline unsigned eytzinger0_last(unsigned size)
+{
+	return eytzinger1_last(size) - 1;
+}
+
+static inline unsigned eytzinger0_next(unsigned i, unsigned size)
+{
+	return eytzinger1_next(i + 1, size) - 1;
+}
+
+static inline unsigned eytzinger0_prev(unsigned i, unsigned size)
+{
+	return eytzinger1_prev(i + 1, size) - 1;
+}
+
+static inline unsigned eytzinger0_extra(unsigned size)
+{
+	return eytzinger1_extra(size);
+}
+
+static inline unsigned __eytzinger0_to_inorder(unsigned i, unsigned size,
+					       unsigned extra)
+{
+	return __eytzinger1_to_inorder(i + 1, size, extra) - 1;
+}
+
+static inline unsigned __inorder_to_eytzinger0(unsigned i, unsigned size,
+					       unsigned extra)
+{
+	return __inorder_to_eytzinger1(i + 1, size, extra) - 1;
+}
+
+static inline unsigned eytzinger0_to_inorder(unsigned i, unsigned size)
+{
+	return __eytzinger0_to_inorder(i, size, eytzinger0_extra(size));
+}
+
+static inline unsigned inorder_to_eytzinger0(unsigned i, unsigned size)
+{
+	return __inorder_to_eytzinger0(i, size, eytzinger0_extra(size));
+}
+
+#define eytzinger0_for_each(_i, _size)			\
+	for (unsigned (_i) = eytzinger0_first((_size));	\
+	     (_i) != -1;				\
+	     (_i) = eytzinger0_next((_i), (_size)))
+
+/* return greatest node <= @search, or -1 if not found */
+static inline int eytzinger0_find_le(void *base, size_t nr, size_t size,
+				     cmp_func_t cmp, const void *search)
+{
+	unsigned i, n = 0;
+
+	if (!nr)
+		return -1;
+
+	do {
+		i = n;
+		n = eytzinger0_child(i, cmp(base + i * size, search) <= 0);
+	} while (n < nr);
+
+	if (n & 1) {
+		/*
+		 * @i was greater than @search, return previous node:
+		 *
+		 * if @i was leftmost/smallest element,
+		 * eytzinger0_prev(eytzinger0_first())) returns -1, as expected
+		 */
+		return eytzinger0_prev(i, nr);
+	} else {
+		return i;
+	}
+}
+
+static inline int eytzinger0_find_gt(void *base, size_t nr, size_t size,
+				     cmp_func_t cmp, const void *search)
+{
+	ssize_t idx = eytzinger0_find_le(base, nr, size, cmp, search);
+
+	/*
+	 * if eytitzinger0_find_le() returned -1 - no element was <= search - we
+	 * want to return the first element; next/prev identities mean this work
+	 * as expected
+	 *
+	 * similarly if find_le() returns last element, we should return -1;
+	 * identities mean this all works out:
+	 */
+	return eytzinger0_next(idx, nr);
+}
+
+static inline int eytzinger0_find_ge(void *base, size_t nr, size_t size,
+				     cmp_func_t cmp, const void *search)
+{
+	ssize_t idx = eytzinger0_find_le(base, nr, size, cmp, search);
+
+	if (idx < nr && !cmp(base + idx * size, search))
+		return idx;
+
+	return eytzinger0_next(idx, nr);
+}
+
+#define eytzinger0_find(base, nr, size, _cmp, search)			\
+({									\
+	void *_base		= (base);				\
+	const void *_search	= (search);				\
+	size_t _nr		= (nr);					\
+	size_t _size		= (size);				\
+	size_t _i		= 0;					\
+	int _res;							\
+									\
+	while (_i < _nr &&						\
+	       (_res = _cmp(_search, _base + _i * _size)))		\
+		_i = eytzinger0_child(_i, _res > 0);			\
+	_i;								\
+})
+
+void eytzinger0_sort_r(void *, size_t, size_t,
+		       cmp_r_func_t, swap_r_func_t, const void *);
+void eytzinger0_sort(void *, size_t, size_t, cmp_func_t, swap_func_t);
+
+#endif /* _EYTZINGER_H */