github.com/SmartMeshFoundation/Spectrum@v0.0.0-20220621030607-452a266fee1e/bmt/bmt_r.go (about)

     1  // Copyright 2017 The Spectrum Authors
     2  // This file is part of the Spectrum library.
     3  //
     4  // The Spectrum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The Spectrum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the Spectrum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  // simple nonconcurrent reference implementation for hashsize segment based
    18  // Binary Merkle tree hash on arbitrary but fixed maximum chunksize
    19  //
    20  // This implementation does not take advantage of any paralellisms and uses
    21  // far more memory than necessary, but it is easy to see that it is correct.
    22  // It can be used for generating test cases for optimized implementations.
    23  // see testBMTHasherCorrectness function in bmt_test.go
    24  package bmt
    25  
    26  import (
    27  	"hash"
    28  )
    29  
    30  // RefHasher is the non-optimized easy to read reference implementation of BMT
    31  type RefHasher struct {
    32  	span    int
    33  	section int
    34  	cap     int
    35  	h       hash.Hash
    36  }
    37  
    38  // NewRefHasher returns a new RefHasher
    39  func NewRefHasher(hasher BaseHasher, count int) *RefHasher {
    40  	h := hasher()
    41  	hashsize := h.Size()
    42  	maxsize := hashsize * count
    43  	c := 2
    44  	for ; c < count; c *= 2 {
    45  	}
    46  	if c > 2 {
    47  		c /= 2
    48  	}
    49  	return &RefHasher{
    50  		section: 2 * hashsize,
    51  		span:    c * hashsize,
    52  		cap:     maxsize,
    53  		h:       h,
    54  	}
    55  }
    56  
    57  // Hash returns the BMT hash of the byte slice
    58  // implements the SwarmHash interface
    59  func (rh *RefHasher) Hash(d []byte) []byte {
    60  	if len(d) > rh.cap {
    61  		d = d[:rh.cap]
    62  	}
    63  
    64  	return rh.hash(d, rh.span)
    65  }
    66  
    67  func (rh *RefHasher) hash(d []byte, s int) []byte {
    68  	l := len(d)
    69  	left := d
    70  	var right []byte
    71  	if l > rh.section {
    72  		for ; s >= l; s /= 2 {
    73  		}
    74  		left = rh.hash(d[:s], s)
    75  		right = d[s:]
    76  		if l-s > rh.section/2 {
    77  			right = rh.hash(right, s)
    78  		}
    79  	}
    80  	defer rh.h.Reset()
    81  	rh.h.Write(left)
    82  	rh.h.Write(right)
    83  	h := rh.h.Sum(nil)
    84  	return h
    85  }