my $depth = 16; # generate 16 Gray codes, 4 bits wide each   
my @gray_codes = ( '0', '1' );
while(scalar(@gray_codes)<$depth)
{
      my @forward_half=map{'0'.$_} @gray_codes;  
      my @reverse_half=map{'1'.$_} reverse @gray_codes);
      @gray_codes=(@forward_half,@reverse_half);
}