#!/usr/bin/perl -w
# hash.pl - Don Yang (uguu.org)
#
# 04/27/08

use strict;

# Trivial hash function.  Not good for most cryptographic use, but
# generates enough randomness for our purpose.
sub Hash($$)
{
   my ($hash, $str) = @_;
   foreach my $c (unpack 'C*', $str)
   {
      $hash = ($hash << 4) ^ ($hash << 1) ^ $c;
   }
   return $hash & 0xffffffff;
}

# Find a usable seed.  "Usable" meaning there is some 00, 01, 10, 11
# sequence available at the same bit positions.
for(my $seed = -99; $seed <= 99; $seed++)
{
   my $z = Hash($seed, "");            # 11
   my $a = Hash($seed, "blackstar");   # 00
   my $b = Hash($seed, "soul");        # 01
   my $c = Hash($seed, "tsubaki");     # 10
   my $d = Hash($seed, "maka");        # 11

   my $diff1 = Hash($seed, "a");
   my $diff2 = Hash($seed, "z");
   my $diff3 = Hash($seed, "aa");
   my $diff4 = Hash($seed, "aaa");

   # Find 2 consecutive 00 bits from XOR all.  This is because
   # 00^01^10^11 == 00.
   my $all = $a ^ $b ^ $c ^ $d;
   for(my $i = 0; $i < 31; $i++)
   {
      if( (($all >> $i) & 3) == 0 )
      {
         # Check that expected bit patterns can be found at each hash
         if( (($z >> $i) & 3) == 3 &&
             (($a >> $i) & 3) == 0 &&
             (($b >> $i) & 3) == 1 &&
             (($c >> $i) & 3) == 2 &&
             (($d >> $i) & 3) == 3 &&
             $diff1 != $diff2 &&
             $diff2 != $diff3 && $diff1 != $diff3 &&
             $diff3 != $diff4 && $diff1 != $diff4 && $diff2 != $diff4 )
         {
            print "seed = $seed, bit = $i\n";
         }
      }
   }
}