[ILUG] Re: un-argh...

[JD Paul]

Hey Kevin,

It looks like you've reinvented the uuencoding algorithm.  (See
http://www.opengroup.org/onlinepubs/7908799/xcu/uuencode.html for a
man page, assuming your local uuencode(1) man page doesn't include the
algorithm.)

Fortunately for your efficiency and fugliness concerns, Perl's pack() and
unpack() already do uuencoding:

$encoded = pack("u*", $s);
$decoded = unpack("u*", $encoded);
if ( $decoded ne $s ) { die "oops!\n"; }

Note the pack/unpack functions simply pass through trailing newlines
(embedded newlines are converted).  This strikes me as very odd --
it makes it hard to emulate the uuencode/uudecode binaries' behavior
-- but at least they're consistent within Perl.

					JD


On Fri, 1 Feb 2002, kevin lyda wrote:

> ok, earlier i posted a question on encoding a string.  i found an answer.
> the goal was to take a string, break it into 6 bit chunks, add 32 to each
> chunk, then spew out the resulting string.  the main characteristic of
> the resulting string is that it would be printable ascii - ascii 32 to 96.
> 
> the solution i came up with is just plain fugly in my opinion, but it
> works and i've spent too much time on this one section of code, so i'm
> sticking with it.  however if someone's bored they can fiddle it to make
> it pretty.  :)
> 
> thanks for all the replies!
> 
>     #!/usr/bin/perl
> 
>     sub encode_string {
> 	my($s) = @_;
> 
> 	my($encoded, $x, $chunk);
> 	$encoded = "";
> 	while (length($s) > 0) {
> 	    $chunk = unpack("b24", $s);
> 	    $s = substr($s, 3);
> 	    foreach $x (1...4){
> 		$encoded .= chr(ord(pack("b6", $chunk)) + 32);
> 		$chunk = substr($chunk, 6);
> 	    }
> 	}
> 	return $encoded;
>     }
> 
>     sub decode_string {
> 	my($e) = @_;
> 
> 	my($decoded, $x, $chunk, $tchunk);
> 	$decoded = "";
> 	while (length($e) > 0) {
> 	    $chunk = unpack("b32", $e);
> 	    $e = substr($e, 4);
> 	    $tchunk = "";
> 	    foreach $x (1...4){
> 		$tchunk .= unpack("b6", chr(ord(pack("b8", $chunk)) - 32));
> 		$chunk = substr($chunk, 8);
> 	    }
> 	    $decoded .= pack("b24", $tchunk);
> 	}
> 	return $decoded;
>     }
> 
>     $s = shift;
>     $s = "\0\0\0AAA".chr(255).chr(255).chr(255)."BBBabcdef";
>     $s .= "\0" x ((length($s) % 3)? 3 - (length($s) % 3): 0);
>     $e = &encode_string($s);
>     $d = &decode_string($e);
> 
>     print("original: '$s' (".length($s).")\n".
> 	  "encoded: '$e'\n".
> 	  "decoded: '$d' (".length($d).")\n");
> 
> kevin
> 
> -- 
> kevin at suberic.net          buffy: come on, can't you put your foot down?!
> fork()'ed on 37058400      giles: it *is* down.
> meatspace place: orbit     buffy: one of these days you're going to have to
> http://suberic.net/~kevin         get a grown up car.  --inca mummy girl
>