Initial commit

vendor/github.com/cockroachdb/pebble/merging_iter_heap.go

@@ -0,0 +1,92 @@
+// Copyright 2018 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package pebble
+
+type mergingIterHeap struct {
+	cmp     Compare
+	reverse bool
+	items   []*mergingIterLevel
+}
+
+func (h *mergingIterHeap) len() int {
+	return len(h.items)
+}
+
+func (h *mergingIterHeap) clear() {
+	h.items = h.items[:0]
+}
+
+func (h *mergingIterHeap) less(i, j int) bool {
+	ikey, jkey := h.items[i].iterKey, h.items[j].iterKey
+	if c := h.cmp(ikey.UserKey, jkey.UserKey); c != 0 {
+		if h.reverse {
+			return c > 0
+		}
+		return c < 0
+	}
+	if h.reverse {
+		return ikey.Trailer < jkey.Trailer
+	}
+	return ikey.Trailer > jkey.Trailer
+}
+
+func (h *mergingIterHeap) swap(i, j int) {
+	h.items[i], h.items[j] = h.items[j], h.items[i]
+}
+
+// init, fix, up and down are copied from the go stdlib.
+func (h *mergingIterHeap) init() {
+	// heapify
+	n := h.len()
+	for i := n/2 - 1; i >= 0; i-- {
+		h.down(i, n)
+	}
+}
+
+func (h *mergingIterHeap) fix(i int) {
+	if !h.down(i, h.len()) {
+		h.up(i)
+	}
+}
+
+func (h *mergingIterHeap) pop() *mergingIterLevel {
+	n := h.len() - 1
+	h.swap(0, n)
+	h.down(0, n)
+	item := h.items[n]
+	h.items = h.items[:n]
+	return item
+}
+
+func (h *mergingIterHeap) up(j int) {
+	for {
+		i := (j - 1) / 2 // parent
+		if i == j || !h.less(j, i) {
+			break
+		}
+		h.swap(i, j)
+		j = i
+	}
+}
+
+func (h *mergingIterHeap) down(i0, n int) bool {
+	i := i0
+	for {
+		j1 := 2*i + 1
+		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
+			break
+		}
+		j := j1 // left child
+		if j2 := j1 + 1; j2 < n && h.less(j2, j1) {
+			j = j2 // = 2*i + 2  // right child
+		}
+		if !h.less(j, i) {
+			break
+		}
+		h.swap(i, j)
+		i = j
+	}
+	return i > i0
+}