Hi bulrush,

Here are a couple of tests, and just for fun my own (horribly inefficient, benchmark included) implementation using Perl's magic string increment:

#!/usr/bin/env perl
use warnings;
use strict;

sub excelpos2ltr { # by bulrush, https://perlmonks.pair.com/?node_id=1
+168549
    my($oldcol)=@_; # Col starts at 0='A'
    my($procname,$numeric,$ltr,$num2,$outs);
    $procname="excelpos2ltr";
    # Alt method 4.
    $numeric = $oldcol % 26;
    $ltr = chr(65 + $numeric);
    #$num2 = intval($oldcol / 26); # old line
    $num2 = int($oldcol / 26);
    if ($num2 > 0) {
        $outs=excelpos2ltr($num2 - 1) . $ltr;
    }
    else {
        $outs=$ltr;
    }
    return $outs;
}

sub colname {
    my $n = "A";
    $n++ for 1..shift;
    return $n;
}

my %tests = (
      0=>"A",    1=>"B",
     25=>"Z",   26=>"AA",
     27=>"AB",  99=>"CV",
    420=>"PE", 479=>"RL",
     14557=>"UMX",
    285075=>"PERL",
);

use Test::More;
plan tests => 2 * scalar keys %tests;
is excelpos2ltr($_), $tests{$_}, "excelpos2ltr $_ => $tests{$_}"
    for sort {$a<=>$b} keys %tests;
is colname($_), $tests{$_}, "colname $_ => $tests{$_}"
    for sort {$a<=>$b} keys %tests;
done_testing;

use Benchmark 'cmpthese';
cmpthese(-5, {
    # not neccesarily a fair benchmark due to random test data
    excelpos2ltr => sub { excelpos2ltr(rand(10000)) },
    colname => sub { colname(rand(10000)) },
});
[download]

Regards,
-- Hauke D