code: func putTxIndexEntry(target []byte, blockID uint32, txLoc wire.TxLoc) {
  	byteOrder.PutUint32(target, blockID)
  	byteOrder.PutUint32(target[4:], uint32(txLoc.TxStart))
  	byteOrder.PutUint32(target[8:], uint32(txLoc.TxLen))
  }
docs: // putTxIndexEntry serializes the provided values according to the format
  // described about for a transaction index entry.  The target byte slice must
  // be at least large enough to handle the number of bytes defined by the
  // txEntrySize constant or it will panic.