#!/usr/bin/perl -w
# table85.pl - Don Yang (uguu.org)
#
# 07/29/12

use strict;

# Assuming that this formula will be used for decoding:
#  orig = (encoded + shift) % mod;
#
# Compute appropriate values for "shift" and "mod" such that all values
# in [0..84] can be covered without using escaping characters.
sub FindDecodeParams()
{
   for(my $shift = 0; $shift < 256; $shift++)
   {
      for(my $mod = 85; $mod < 94; $mod++)
      {
         my %uniq;
         for(my $c = 33; $c < 127; $c++)
         {
            next if (chr($c) eq '"' || chr($c) eq '\\');
            $uniq{($c + $shift) % $mod}++;
         }

         my $accept = 1;
         for(my $i = 0; $i < 85; $i++)
         {
            unless( exists $uniq{$i} )
            {
               $accept = 0;
               last;
            }
         }

         if( $accept )
         {
            print "shift=$shift, mod=$mod\n";
         }
      }
   }
}

# Output decode table to stdout
sub OutputTable($$)
{
   my ($shift, $mod) = @_;

   for(my $i = 33; $i < 127; $i++)
   {
      next if (chr($i) eq '"' || chr($i) eq '\\');
      my $o = ($i + $shift) % $mod;
      next if( $o >= 85 );
      printf '%03d %c -> %03d'."\n", $i, $i, $o;
   }
}

OutputTable(83, 89);