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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package merklearray
import (
"fmt"
"hash"
"github.com/algorand/go-algorand/crypto"
)
// siblings represents the siblings needed to compute the root hash
// given a set of leaf nodes. This data structure can operate in two
// modes: either build up the set of sibling hints, if tree is not nil,
// or use the set of sibling hints, if tree is nil.
type siblings struct {
tree *Tree
hints []crypto.GenericDigest
}
// get returns the sibling from tree level l (0 being the leaves)
// position i.
func (s *siblings) get(l uint64, i uint64) (res crypto.GenericDigest, err error) {
if s.tree == nil {
if len(s.hints) > 0 {
res = s.hints[0].ToSlice()
s.hints = s.hints[1:]
return
}
err = fmt.Errorf("no more sibling hints")
return
}
if l >= uint64(len(s.tree.Levels)) {
err = fmt.Errorf("level %d beyond tree height %d", l, len(s.tree.Levels))
return
}
if i < uint64(len(s.tree.Levels[l])) {
res = s.tree.Levels[l][i]
}
s.hints = append(s.hints, res)
return
}
// partialLayer represents a subset of a Layer (i.e., nodes at some
// level in the Merkle tree). layerItem represents one element in the
// partial Layer.
//
//msgp:ignore partialLayer
type partialLayer []layerItem
type layerItem struct {
pos uint64
hash crypto.GenericDigest
}
// up takes a partial Layer at level l, and returns the next-higher (partial)
// level in the tree. Since the Layer is partial, up() requires siblings.
//
// The implementation is deterministic to ensure that up() asks for siblings
// in the same order both when generating a proof, as well as when checking
// the proof.
//
// If doHash is false, fill in zero hashes, which suffices for constructing
// a proof.
func (pl partialLayer) up(s *siblings, l uint64, doHash bool, hsh hash.Hash) (partialLayer, error) {
var res partialLayer
for i := 0; i < len(pl); i++ {
item := pl[i]
pos := item.pos
posHash := item.hash
siblingPos := pos ^ 1
var siblingHash crypto.GenericDigest
if i+1 < len(pl) && pl[i+1].pos == siblingPos {
// If our sibling is also in the partial Layer, use its
// hash (and skip over its position).
siblingHash = pl[i+1].hash
i++
} else {
// Ask for the sibling hash from the tree / proof.
var err error
siblingHash, err = s.get(l, siblingPos)
if err != nil {
return nil, err
}
}
nextLayerPos := pos / 2
var nextLayerHash crypto.GenericDigest
if doHash {
var p pair
p.hashDigestSize = hsh.Size()
if pos&1 == 0 {
// We are left
p.l = posHash
p.r = siblingHash
} else {
// We are right
p.l = siblingHash
p.r = posHash
}
nextLayerHash = crypto.GenericHashObj(hsh, p)
}
res = append(res, layerItem{
pos: nextLayerPos,
hash: nextLayerHash,
})
}
return res, nil
}
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