github.com/arieschain/arieschain@v0.0.0-20191023063405-37c074544356/bmt/bmt_r.go (about)

     1  // simple nonconcurrent reference implementation for hashsize segment based
     2  // Binary Merkle tree hash on arbitrary but fixed maximum chunksize
     3  // This implementation does not take advantage of any paralellisms and uses
     4  // far more memory than necessary, but it is easy to see that it is correct.
     5  // It can be used for generating test cases for optimized implementations.
     6  // see testBMTHasherCorrectness function in bmt_test.go
     7  package bmt
     8  
     9  import (
    10  	"hash"
    11  )
    12  
    13  // RefHasher is the non-optimized easy to read reference implementation of BMT
    14  type RefHasher struct {
    15  	span    int
    16  	section int
    17  	cap     int
    18  	h       hash.Hash
    19  }
    20  
    21  // NewRefHasher returns a new RefHasher
    22  func NewRefHasher(hasher BaseHasher, count int) *RefHasher {
    23  	h := hasher()
    24  	hashsize := h.Size()
    25  	maxsize := hashsize * count
    26  	c := 2
    27  	for ; c < count; c *= 2 {
    28  	}
    29  	if c > 2 {
    30  		c /= 2
    31  	}
    32  	return &RefHasher{
    33  		section: 2 * hashsize,
    34  		span:    c * hashsize,
    35  		cap:     maxsize,
    36  		h:       h,
    37  	}
    38  }
    39  
    40  // Hash returns the BMT hash of the byte slice
    41  // implements the SwarmHash interface
    42  func (rh *RefHasher) Hash(d []byte) []byte {
    43  	if len(d) > rh.cap {
    44  		d = d[:rh.cap]
    45  	}
    46  
    47  	return rh.hash(d, rh.span)
    48  }
    49  
    50  func (rh *RefHasher) hash(d []byte, s int) []byte {
    51  	l := len(d)
    52  	left := d
    53  	var right []byte
    54  	if l > rh.section {
    55  		for ; s >= l; s /= 2 {
    56  		}
    57  		left = rh.hash(d[:s], s)
    58  		right = d[s:]
    59  		if l-s > rh.section/2 {
    60  			right = rh.hash(right, s)
    61  		}
    62  	}
    63  	defer rh.h.Reset()
    64  	rh.h.Write(left)
    65  	rh.h.Write(right)
    66  	h := rh.h.Sum(nil)
    67  	return h
    68  }