Commit 598a18a3 authored by Kirill Smelkov's avatar Kirill Smelkov

.

parent 650ec24f
// Copyright (c) 2001, 2002 Zope Foundation and Contributors.
// All Rights Reserved.
//
// This software is subject to the provisions of the Zope Public License,
// Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution.
// THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
// WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
// FOR A PARTICULAR PURPOSE
//
// XXX clarify on licensing (ZPL for BTrees)
//
// Copyright (C) 2018 Nexedi SA and Contributors.
// Kirill Smelkov <kirr@nexedi.com>
//
......@@ -34,7 +46,7 @@ import (
// XXX start from loading ZBigFile btree
// ZBigFile mimics ZBigFile from python.
type ZBigFile struct {
pyobj *zodb.PyObject
......@@ -86,3 +98,148 @@ func (conn *zpyconn) loadZBigFile(ctx context.Context, oid zodb.Oid) (*ZBigFile,
// XXX ok
}
// ZBucket mimics ?OBucket from btree/py, with ? being any integer.
//
// py description:
//
// A Bucket wraps contiguous vectors of keys and values. Keys are unique,
// and stored in sorted order. The 'values' pointer may be NULL if the
// Bucket is used to implement a set. Buckets serving as leafs of BTrees
// are chained together via 'next', so that the entire BTree contents
// can be traversed in sorted order quickly and easily.
type ZBucket struct {
pyobj *zodb.PyObject
next *ZBucket // the bucket with the next-larger keys
keys []KEY // 'len' keys, in increasing order
values []interface{} // 'len' corresponding values XXX merge k/v ?
}
// zBTreeItem mimics BTreeItem from btree/py.
type zBTreeItem {
key KEY
child interface{} // ZBTree or ZBucket
}
// ZBTree mimics ?OBTree from btree/py, with ? being any integer.
//
// See https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/Development.txt#L198
// for details.
type ZBTree struct {
pyobj *zodb.PyObject
// firstbucket points to the bucket containing the smallest key in
// the BTree. This is found by traversing leftmost child pointers
// (data[0].child) until reaching a Bucket.
firstbucket *ZBucket
// The BTree points to 'len' children, via the "child" fields of the data
// array. There are len-1 keys in the 'key' fields, stored in increasing
// order. data[0].key is unused. For i in 0 .. len-1, all keys reachable
// from data[i].child are >= data[i].key and < data[i+1].key, at the
// endpoints pretending that data[0].key is minus infinity and
// data[len].key is positive infinity.
data []zBTreeItem
}
// Get searches BTree by key.
//
// It loads intermediate BTree nodes from database on demand as needed.
// XXX ok -> ErrKeyNotFound?
func (t *ZBTree) Get(ctx context.Context, key KEY) (interface{}, bool, error) {
t.PActivate(ctx) // XXX err
if len(t.data) == 0 {
// empty btree
return nil, false, nil
}
for {
// search i: K(i) ≤ k < K(i+1) ; K(0) = -∞, K(len) = +∞
i := sort.Search(len(t.data), func(i int) bool {
j := i + 1
if j == len(t.data) {
return true // [len].key = +∞
}
return key < t.data[j].key
})
switch child := t.data[i].child.(type) {
case *ZBTree:
// XXX t.PAllowDeactivate
t = child
t.PActivate(ctx) // XXX err
case *ZBucket:
child.PActivate(ctx) // XXX err
return child.Get(key), nil
}
}
}
// get searches Bucket by key.
//
// no loading from database is done. The bucket must be already activated.
func (b *ZBucket) get(key KEY) (interface{}, bool) {
// XXX b.PActivate ? XXX better caller? (or inside if get -> Get)
// search i: K(i-1) < k ≤ K(i) ; K(-1) = -∞, K(len) = +∞
i := sort.Search(len(b.keys), func(i int) bool {
return key <= t.data[i].key
})
if i == len(b.keys) || b.keys[i] != key {
return nil, false // not found
}
return b.values[i], true
}
// from https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/BTreeTemplate.c#L1087:
//
// For an empty BTree (self->len == 0), None.
//
// For a BTree with one child (self->len == 1), and that child is a bucket,
// and that bucket has a NULL oid, a one-tuple containing a one-tuple
// containing the bucket's state:
//
// (
// (
// child[0].__getstate__(),
// ),
// )
//
// Else a two-tuple. The first element is a tuple interleaving the BTree's
// keys and direct children, of size 2*self->len - 1 (key[0] is unused and
// is not saved). The second element is the firstbucket:
//
// (
// (child[0], key[1], child[1], key[2], child[2], ...,
// key[len-1], child[len-1]),
// self->firstbucket
// )
//
// In the above, key[i] means self->data[i].key, and similarly for child[i].
// XXX ZBTree.Get(key)
// XXX ZBucket.MinKey ?
// XXX ZBucket.MaxKey ?
// from https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/BucketTemplate.c#L1195:
//
// For a mapping bucket (self->values is not NULL), a one-tuple or two-tuple.
// The first element is a tuple interleaving keys and values, of length
// 2 * self->len. The second element is the next bucket, present iff next is
// non-NULL:
//
// (
// (keys[0], values[0], keys[1], values[1], ...,
// keys[len-1], values[len-1]),
// <self->next iff non-NULL>
// )
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