my $data = "1024 bytes of data from the file";
my $odd = "";
my $even = "";
for my $bitpair (0..(4 * length $data - 1)) {
  my $twobits = vec($data, $bitpair, 2);
  vec($odd, $bitpair, 1) = 1 if $twobits & 2;
  vec($even, $bitpair, 1) = 1 if $twobits & 1;
}