But other characters would be acceptable if it makes compressin possible.

If you have a case sensitive system, that's 64 safe characters. If you can compressed (by packing numbers or otherwise) the data down to 33 bytes (floor((90/2) * (log2(64)/8))), you could use the following to convert to safe characters:

use MIME::Base64;

sub encode {
   my ($compressed) = @_;
   my $encoded = encode_base64($compressed);
   $encoded =~ s{\+}{-}g;
   $encoded =~ s{\/}{_}g;
   return $encoded;
}

sub decode {
   my ($encoded) = @_;
   $encoded =~ s{-}{+}g;
   $encoded =~ s{_}{/}g;
   my $compressed = decode_base64($encoded);
   return $compressed;
}
[download]

Update: On second thought, if people are gong to save these files on their own PCs, you'll need to be case-insensitive. That leaves 38 safe characters. If you wrote Base32 based on Base64 (a simple task), you'll have to compress the data down to 28 bytes (floor((90/2) * (log2(32)/8))).

Update: Fixed attrocious math.

Original filename was 125 characters.

"Compressed" filename is 175 characters.




Forget that fear of gravity,
Get a little savagery in your life.

As you've seen, with 64 characters in the input, that 90*6-bits = 67.5 (mostly unacceptable) 8-bit chars as your best "simple transform' compression. A bare 2/3rds compression, even if all the 8-bit chars were acceptable in a filename which the aren't.

Your best hope is if your filenames can be split into various fields that can be represented by a number that is shorter than the fields text representation. For example: if one component of the name was one of 'North', 'NorthEast', 'East', 'SouthEast', 'South', 'SouthWest', 'West', 'NorthWest', that same field could be replaced by a digit 0-7, or maybe just 4-bits in conjunction with some other field with upto 3-bits.

Without seeing examples of the filenames, and the range of values the fields within represent, it's hard to be more helpful.

---

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Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?

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In the absence of evidence, opinion is indistinguishable from prejudice.

Edit: g0n - reparented at authors request