DB<138> undef $m0; vec($m0,$_,1)=1 for  0,2,8,9,10

  DB<139> p unpack('b16', $m0)                    # ok LSB left
1010000011100000
  DB<140> p unpack('B16', $m0)                    # MSB, but inside LS bytes chunks
0000010100000111
  DB<142> $x+= 2**$_ for  0,2,8,9,10

  DB<144> printf "%016b",$x                      # what I expected
0000011100000101
  DB<145>

##</code><code>##

   B  A bit string (descending bit order inside each byte).

##</code><code>##

  DB<184> p reverse unpack ('B8B8',$m0)
0000011100000101
  DB<185>