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// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// Package bmt is a simple nonconcurrent reference implementation for hashsize segment based
// Binary Merkle tree hash on arbitrary but fixed maximum chunksize
//
// This implementation does not take advantage of any paralellisms and uses
// far more memory than necessary, but it is easy to see that it is correct.
// It can be used for generating test cases for optimized implementations.
// see testBMTHasherCorrectness function in bmt_test.go
package bmt
import (
"hash"
)
// RefHasher is the non-optimized easy to read reference implementation of BMT
type RefHasher struct {
span int
section int
cap int
h hash.Hash
}
// NewRefHasher returns a new RefHasher
func NewRefHasher(hasher BaseHasher, count int) *RefHasher {
h := hasher()
hashsize := h.Size()
maxsize := hashsize * count
c := 2
for ; c < count; c *= 2 {
}
if c > 2 {
c /= 2
}
return &RefHasher{
section: 2 * hashsize,
span: c * hashsize,
cap: maxsize,
h: h,
}
}
// Hash returns the BMT hash of the byte slice
// implements the SwarmHash interface
func (rh *RefHasher) Hash(d []byte) []byte {
if len(d) > rh.cap {
d = d[:rh.cap]
}
return rh.hash(d, rh.span)
}
func (rh *RefHasher) hash(d []byte, s int) []byte {
l := len(d)
left := d
var right []byte
if l > rh.section {
for ; s >= l; s /= 2 {
}
left = rh.hash(d[:s], s)
right = d[s:]
if l-s > rh.section/2 {
right = rh.hash(right, s)
}
}
defer rh.h.Reset()
rh.h.Write(left)
rh.h.Write(right)
h := rh.h.Sum(nil)
return h
}
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