    # File lib/fog/aws/glacier.rb, line 45
            def reduce_digests(digests)
              while digests.length > 1
                digests = digests.each_slice(2).collect do |pair|
                  if pair.length == 2
                    Digest::SHA256.digest(pair[0]+pair[1])
                  else
                    pair.first
                  end
                end
              end
              digests.first
            end