my @SetBits= ( [], [0], [1], [0,1], [2], [0,2],
  [1,2], [3], [0,3] ...

...

sub findsetbits { #feed with array of bytes
  my @result;
  my $offset=0;
  foreach my $byte (@_) {
    foreach (@{$SetBits[$byte]}) {
      push @result, $_+$offset;
    }
    $offset+= 8;
  }
  return @result;
}