wcfs: xbtree: blib: Start of package

This will be the place to keep BTree-related utilities.
For now it provides only type aliases since Go lacks generics.

wcfs/internal/xbtree/blib/blib.go

+// Copyright (C) 2021  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+// Package blib provides utilities related to BTrees.
+package blib
+
+import (
+	"fmt"
+	"math"
+
+	"lab.nexedi.com/kirr/neo/go/zodb/btree"
+)
+
+// XXX instead of generics
+type Tree   = btree.LOBTree
+type Bucket = btree.LOBucket
+type Node   = btree.LONode
+type TreeEntry   = btree.LOEntry
+type BucketEntry = btree.LOBucketEntry
+
+type Key         = int64
+type KeyRange    = btree.LKeyRange
+const KeyMax Key = math.MaxInt64
+const KeyMin Key = math.MinInt64
+
+
+// KStr formats key as string.
+func KStr(k Key) string {
+	if k == KeyMin {
+		return "-∞"
+	}
+	if k == KeyMax {
+		return "∞"
+	}
+	return fmt.Sprintf("%d", k)
+}