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Re: Merge CIDRs

by gbarr (Monk)
on Oct 13, 2001 at 04:31 UTC ( #118610=note: print w/replies, xml ) Need Help??

in reply to Merge CIDRs

Looking at this and considering my own post, I thought I would try to improve it. The following code allows trailing zeros to be left off the input CIDR and it will leave off the trailing zeros in the output. It also handles 0/0, which neither of our posts did

use strict; sub cidr2bits { my $cidr = shift; my $n = $cidr =~ s,/(\d+)$, ? $1 : 32; my @n = $cidr =~ m,\d+,g; substr(unpack("B*",pack("C4", @n,0,0,0,0)),0,$n); } sub bits2cidr { my $bits = shift; my $n = length $bits; $bits .= "0" x 8; join(".", unpack("C*", pack("B*",($bits =~ /^((?:.{8})+?)0*$/)[0]))) +."/$n"; } sub mergecidr { local $_ = join("\n", sort map { cidr2bits($_) } @_); 1 while s/^(\d*)\n\1.*$/$1/mg || s/^(\d*)0\n\1.$/$1/mg; map { bits2cidr($_) } (!@_ || length($_)) ? split : ''; }

Update: Swapped the two s/// in the while to prevent the problem merlyn described. Now in the case of

10010 100100 100101

the first two lines will be merged first and yeild the correct result

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Re: Re: Merge CIDRs
by merlyn (Sage) on Oct 13, 2001 at 05:24 UTC
    1 while s/^(\d*)0\n\1.$/$1/mg || s/^(\d*)\n\1.*$/$1/mg;
    There's a reason I put [1] there instead of your ".". Consider what happens when you have the following:
    10010 100100 100101
    The last two lines will be merged, creating
    10010 10010
    And your code will strip that final 0 from both lines, creating "1001". Wrong. You must ensure that it's a 1. Can't be "any".

    -- Randal L. Schwartz, Perl hacker

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