path: root/bmt/bmt_r.go

// 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/>.

// 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
}