getmask

#!/usr/bin/perl
#-------------------------------------------------------------------------------

sub bitmask {
	local ($low,$high,$top)=(@_);

	return if($low>$high);
	# get highest bit needed for calculation
	if($top eq ""){
		for($top=1;$top<$high;$top*=2){}
	}
	for(local $i=$top;$i>=1;$i/=2) {
		for(local $j=0;$j<=$top;$j+=$i) {
			if($j>=$low&&$j+$i-1<=$high) {
				return(&bitmask($low,$j-1,$top),
				"$j-". ( $j + ( $i - 1 ) ) ."/$i",
				&bitmask($j+$i,$high,$top));
			}
		}
	}
}

for(@ARGV) {
	/^[0-9]+-[0-9]+$/ && do {
		@a=split("-",$_);
		if($a[0]>$a[1]) {
			warn "first number must be smaller in a sequence\n";
			next;
		}
		print "[$a[0]-$a[1]]\n";
		print " ".join("\n ",&bitmask(@a))."\n";
		next;
	};
	warn "\"$_\" not expected\n";
}