Re: On Tabs and Spaces

From: Nikolai Weibull <now@bitwi.se>
Date: Oct 17, 2007, 10:21 UTC
Message-ID: <dbfc82860710170321l458ebd1cr6bf619cef9bb7300@mail.gmail.com>
In-Reply-To: <E29971BA-7306-4570-8383-26D0C9C0B814@mit.edu>

On 10/17/07, Michael Witten <mfwitten@mit.edu> wrote:

Show 30 quoted lines

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