DB<315> undef $m1; vec($m1,$_,1)=1 for 0,2,8,9,10

  DB<316> x unpack 'b16',$m1
0  1010000011100000
  DB<317> p reverse unpack 'b16',$m1
1010000011100000
  DB<318> p scalar reverse unpack 'b16',$m1
0000011100000101
  DB<319>