I'm not entirely sure what is going on here.
Although its a particularly messy piece of code it does actually work! I was concerned by the results you got so I re-ran the code myself and was unable to get the same results.
Because I am lazy I missed off the -w and use strict in the code I posted (in my actual code everthing is a little more strict). It could be something to do with this that causes the effect you have seen. Although with -w I do not get any errors and it works OK. Try this: 
#!/usr/local/bin/perl -w

use strict;

my $desc = "I %2Blike %3A cheese";
my ($str, @ob);

print "TEST: ",test(),"\n";<br>

sub test {
    $_ = $desc;
    while (/%[0-9A-Za-z]{2}/) {
        $_ = $&;
        /[0-9A-Za-z]{2}/;
        $ob[0] = hex($&);
        $str = pack("C*", @ob);
        $desc =~ s/%[0-9A-Za-z]{2}/$str/;
        $_ = $desc;
        }
    return $desc;
}

returns:

TEST: I +like : cheese

[download]
This definitely works OK for me.
UPDATE: My apologies, I've just noticed what was wrong with the code that I originally posted. $name is not initially set up - so the loop runs through 1 iteration and fails. As I didn't want to actually change $str I changed the code a little - but forgot check it properly. This should work: 
...
'myway' => sub {
    $_ = $str;
    $name = $str;
    while (/%[0-9A-Fa-f]{2}/) {
       $_ = $&;
...

[download]
I guess the lessons learnt are: BTW the new benchmark timings are:
Benchmark: timing 500000 iterations of myway, regexpway...
     myway: 162 wallclock secs (162.07 usr +  0.00 sys = 162.07 CPU)
 regexpway: 58 wallclock secs (58.52 usr +  0.01 sys = 58.53 CPU)

[download]
which make a lot more sense.
I now feel older, wiser and more than a little bit stupid.

In reply to RE: RE: RE: form parsing, hex, HTML formatting by muppetBoy
in thread form parsing, hex, HTML formatting by Anonymous Monk

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