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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 (
"errors"
"fmt"
"math/bits"
"github.com/algorand/go-algorand/crypto"
"github.com/algorand/go-algorand/protocol"
)
// ErrGetOutOfBound returned when trying to retrieve an element which is out of the padded array bound.
var (
ErrGetOutOfBound = errors.New("can't get element out of padded array bound")
)
type vectorCommitmentArray struct {
array Array
pathLen uint8
paddedLen uint64
}
type bottomElement struct{}
func (b *bottomElement) ToBeHashed() (protocol.HashID, []byte) {
return protocol.MerkleVectorCommitmentBottomLeaf, []byte{}
}
func generateVectorCommitmentArray(innerArray Array) *vectorCommitmentArray {
arrayLen := innerArray.Length()
if arrayLen == 0 || arrayLen == 1 {
return &vectorCommitmentArray{array: innerArray, pathLen: 1, paddedLen: 1}
}
path := uint8(bits.Len64(arrayLen - 1))
fullSize := uint64(1 << path)
return &vectorCommitmentArray{array: innerArray, pathLen: path, paddedLen: fullSize}
}
func (vc *vectorCommitmentArray) Length() uint64 {
return vc.paddedLen
}
func (vc *vectorCommitmentArray) Marshal(pos uint64) (crypto.Hashable, error) {
lsbIndex, err := merkleTreeToVectorCommitmentIndex(pos, vc.pathLen)
if err != nil {
return nil, err
}
if lsbIndex >= vc.paddedLen {
return nil, fmt.Errorf("vectorCommitmentArray.Get(%d): out of bounds, full size %d: %w", pos, vc.paddedLen, ErrGetOutOfBound)
}
if lsbIndex < vc.array.Length() {
return vc.array.Marshal(lsbIndex)
}
return &bottomElement{}, nil
}
// merkleTreeToVectorCommitmentIndex Translate an index of an element on a merkle tree to an index on the vector commitment.
// The given index must be within the range of the elements in the tree (assume this number is 1^pathLen)
func merkleTreeToVectorCommitmentIndex(msbIndex uint64, pathLen uint8) (uint64, error) {
if msbIndex >= (1 << pathLen) {
return 0, fmt.Errorf("msbIndex %d >= 1^pathLen %d: %w", msbIndex, 1<<pathLen, ErrPosOutOfBound)
}
return bits.Reverse64(msbIndex) >> (64 - pathLen), nil
}
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