[geek] How apache 2's autoindex converts bytes to kilobytes and megabytes.

[darxus]

This was tedious to figure out, so hopefully I can spare someone else. In perl:

if ($sizeunit eq 'K') {
  $realsize = round($realsize/1024);
} elsif ($sizeunit eq 'M') {
  $realsize = round($realsize/1024/1024);
}

sub round {
  my($number) = shift;
  my $left = (split('\.',$number))[0];
  if (length($left) <= 1) {
    return int( $number * 10 + .5 )/10;
  } else {
    return int( $number + .5 );
  }
}

I'm convinced there is no simpler way (I read the whole sprintf man page at least twice).

I'm writing a monitoring script that checks the sizes of files on a web server. So I figured I should do a little random validation that apache is reporting the same file size that I'm getting from length($content). So I needed to convert length($content) to the same form I get from apache.

Comments

[ectropy.livejournal.com]

There's no way to include such basic math functions as Round() or use the modulo operator?

[darxus.livejournal.com]

Perl has no round(). The faq entry tells you how to write it. I'm not great with modulo, so it's not obvious to me how it would be useful.

how to do it with sprintf

[cos]

if ($sizeunit eq 'K') {
  $realsize = sprintf("%d",$realsize/1024 +.5);
} elsif ($sizeunit eq 'M') {
  $realsize = sprintf("%d",$realsize/1024/1024 +.5);
}

real rounding with sprintf

[cos]

Oops, I forgot the floating point conversation always does real rounding, so another way is:

$rounded = sprintf("%.0f", $number/1024);

Re: real rounding with sprintf

[darxus.livejournal.com]

You skipped the variable precision.

Re: real rounding with sprintf

[cos]

Ahh, I see what you're saying. Something like this?

$size /= 1024;
$pr = $size<9.5 ? 1 : 0;
$round = sprintf("%.${pr}", $size);

Re: real rounding with sprintf

[darxus.livejournal.com]

Looks likely to work.

Re: real rounding with sprintf

[feng-huang.livejournal.com]

Hmm... I can't remember where the discussion was (aside from "somebody else's journal), but I got chided semi-recently for suggesting sprintf as a method of rounding. The other person said it was slow and error-prone. I can't recall if I asked for a reference for this claim. I'll try to remember where this discussion took place and see if there was anything to substantiate the other person's claim.

Re: real rounding with sprintf

[cos]

You could do $rounded = int($num+.5) but he mentioned sprintf specifically. For variable precision sprintf is easier, and I highly doubt rounding performance is a big issue in this kind of application.