my $h = unpack( 'H*', $bitstring ) ;

##</code><code>##

  my $h = unpack( 'H*', scalar reverse $bitstring ) ;

##</code><code>##

  my $h = unpack( 'H*', pack('b*', unpack('B*', $bitstring)) ) ;

##</code><code>##

  my $h = unpack( 'H*', pack('b*', unpack('B*', scalar reverse $bitstring)) ) ;