Re: On Tabs and Spaces

On 10/17/07, Michael Witten [off-list ref] wrote:

On 17 Oct 2007, at 3:17:08 AM, Luke Lu wrote:

quoted

But I still haven't seen any compelling arguments against the "all
space" case

Overhead!

If you use 8 spaces instead of one tab,
that's using up 7x more space!

Consider:

     # calculates the extra space required to
     # use the given number of spaces/tab.
     size()
     {
         count=`grep -RIo "\`printf \"\t\"\`" . | wc -l`;
         perl -e "print $count*$(($1-1))/1024/1024 . \" MB\n\"";
     }

     Then in in a git working tree:

         size 8; # 1.28701210021973 MB
         size 4; # 0.551576614379883 MB

     In a linux kernel working tree:

         size 8; # 61.4902725219727 MB
         size 4; # 26.3529739379883 MB

As already pointed out, this isn't the true waste.  Run the following
Ruby script to determine the true waste:

------------ cut here -----------
TabWidth = 8

actual_size = 0
expanded_size = 0
ARGF.each_line do |line|
  width = 0
  line.each_byte do |byte|
    width += (byte == ?\t) ? (TabWidth - (width % TabWidth)) : 1
  end
  actual_size += line.length
  expanded_size += width
end
puts (expanded_size - actual_size).to_s
------------ cut here -----------

This will give you the actual space waste.  Run it like so:

% ruby space-waste.rb /usr/src/linux/**/*.[ch]

(or in a similar manner that doesn't fail due to going over the
maximum command-line limit).

According to this calculation the waste is 47808782 bytes, or about
45.6 MiB, for 8-spaces-wide tabs.