github.com/anacrolix/torrent@v1.61.0/merkle/merkle.go (about)

     1  package merkle
     2  
     3  import (
     4  	"crypto/sha256"
     5  	"fmt"
     6  	"math/bits"
     7  
     8  	g "github.com/anacrolix/generics"
     9  )
    10  
    11  // The leaf block size for BitTorrent v2 Merkle trees.
    12  const BlockSize = 1 << 14 // 16KiB
    13  
    14  func Root(hashes [][sha256.Size]byte) [sha256.Size]byte {
    15  	switch len(hashes) {
    16  	case 0:
    17  		return sha256.Sum256(nil)
    18  	case 1:
    19  		return hashes[0]
    20  	}
    21  	numHashes := uint(len(hashes))
    22  	if numHashes != RoundUpToPowerOfTwo(uint(len(hashes))) {
    23  		panic(fmt.Sprintf("expected power of two number of hashes, got %d", numHashes))
    24  	}
    25  	var next [][sha256.Size]byte
    26  	for i := 0; i < len(hashes); i += 2 {
    27  		left := hashes[i]
    28  		right := hashes[i+1]
    29  		h := sha256.Sum256(append(left[:], right[:]...))
    30  		next = append(next, h)
    31  	}
    32  	return Root(next)
    33  }
    34  
    35  func RootWithPadHash(hashes [][sha256.Size]byte, padHash [sha256.Size]byte) [sha256.Size]byte {
    36  	for uint(len(hashes)) < RoundUpToPowerOfTwo(uint(len(hashes))) {
    37  		hashes = append(hashes, padHash)
    38  	}
    39  	return Root(hashes)
    40  }
    41  
    42  func CompactLayerToSliceHashes(compactLayer string) (hashes [][sha256.Size]byte, err error) {
    43  	g.MakeSliceWithLength(&hashes, len(compactLayer)/sha256.Size)
    44  	for i := range hashes {
    45  		n := copy(hashes[i][:], compactLayer[i*sha256.Size:])
    46  		if n != sha256.Size {
    47  			err = fmt.Errorf("compact layer has incomplete hash at index %d", i)
    48  			return
    49  		}
    50  	}
    51  	return
    52  }
    53  
    54  func RoundUpToPowerOfTwo(n uint) (ret uint) {
    55  	return 1 << bits.Len(n-1)
    56  }
    57  
    58  func Log2RoundingUp(n uint) (ret uint) {
    59  	return uint(bits.Len(n - 1))
    60  }