$ perl -E'say int( log(562949953421309) / log(2) )'
48

$ perl -E'say int( log(562949953421310) / log(2) )'
49     XXX

$ perl -E'say int( log(562949953421311) / log(2) )'
49     XXX

$ perl -E'say int( log(562949953421312) / log(2) )'
49

$ perl -E'say int( log(562949953421313) / log(2) )'
49