1 files changed, 85 insertions, 0 deletions
diff --git a/swarm/bmt/bmt_r.go b/swarm/bmt/bmt_r.go
new file mode 100644
index 000000000..c61d2dc73
--- /dev/null
+++ b/swarm/bmt/bmt_r.go
@@ -0,0 +1,85 @@
+// 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.
+// There is extra check on reference hasher correctness in bmt_test.go
+// * TestRefHasher
+// * testBMTHasherCorrectness function
+package bmt
+
+import (
+	"hash"
+)
+
+// RefHasher is the non-optimized easy-to-read reference implementation of BMT
+type RefHasher struct {
+	maxDataLength int       // c * hashSize, where c = 2 ^ ceil(log2(count)), where count = ceil(length / hashSize)
+	sectionLength int       // 2 * hashSize
+	hasher        hash.Hash // base hash func (Keccak256 SHA3)
+}
+
+// NewRefHasher returns a new RefHasher
+func NewRefHasher(hasher BaseHasherFunc, count int) *RefHasher {
+	h := hasher()
+	hashsize := h.Size()
+	c := 2
+	for ; c < count; c *= 2 {
+	}
+	return &RefHasher{
+		sectionLength: 2 * hashsize,
+		maxDataLength: c * hashsize,
+		hasher:        h,
+	}
+}
+
+// Hash returns the BMT hash of the byte slice
+// implements the SwarmHash interface
+func (rh *RefHasher) Hash(data []byte) []byte {
+	// if data is shorter than the base length (maxDataLength), we provide padding with zeros
+	d := make([]byte, rh.maxDataLength)
+	length := len(data)
+	if length > rh.maxDataLength {
+		length = rh.maxDataLength
+	}
+	copy(d, data[:length])
+	return rh.hash(d, rh.maxDataLength)
+}
+
+// data has length maxDataLength = segmentSize * 2^k
+// hash calls itself recursively on both halves of the given slice
+// concatenates the results, and returns the hash of that
+// if the length of d is 2 * segmentSize then just returns the hash of that section
+func (rh *RefHasher) hash(data []byte, length int) []byte {
+	var section []byte
+	if length == rh.sectionLength {
+		// section contains two data segments (d)
+		section = data
+	} else {
+		// section contains hashes of left and right BMT subtreea
+		// to be calculated by calling hash recursively on left and right half of d
+		length /= 2
+		section = append(rh.hash(data[:length], length), rh.hash(data[length:], length)...)
+	}
+	rh.hasher.Reset()
+	rh.hasher.Write(section)
+	s := rh.hasher.Sum(nil)
+	return s
+}