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    return $GOT_BIGINT = eval 'use Math::BigInt; 1' ? 1 : 0;
  }
}

sub _alpha_encode {
  my ( $self, $data, $bytes ) = @_;
  my $code;

  if ( _got_bigint() && $bytes > 4 ) {
    # Make a big hex constant
    $code = Math::BigInt->new(
      '0x'
       . join( '',
        map { sprintf( "%02x", ord( $_ ) ) } reverse split //, $data )
    );
  }
  else {
    $code = unpack( 'V', $data . "\0" x ( 4 - length $data ) );
  }

  my $limit = 2**( $bytes * 8 );

  my @alphabet   = split //, $self->alphabet;
  my $code_space = @alphabet;
  my @out        = ();
  my $max        = 1;

  while ( $max < $limit ) {
    push @out, $alphabet[ $code % $code_space ];
    $code = int( $code / $code_space );
    $max *= $code_space;
  }

  return join '', @out;
}

1;
__END__

=head1 CONFIGURATION AND ENVIRONMENT
  
Crypt::PerfectPaperPasswords requires no configuration files or environment variables.

=head1 DEPENDENCIES

L<Crypt::Rijndael>

L<Digest::SHA256>

L<Scalar::Util>

L<Time::HiRes>

L<Math::BigInt> (optional)


=head1 INCOMPATIBILITIES

None reported.

=head1 BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to
C<bug-crypt-perfectpaperpasswords@rt.cpan.org>, or through the web interface at
L<http://rt.cpan.org>.

=head1 AUTHOR

Andy Armstrong  C<< <andy@hexten.net> >>

Original Perfect Paper Passwords implementation by Steve Gibson. More details
here:

    http://www.grc.com/ppp.htm

=head1 LICENCE AND COPYRIGHT

Copyright (c) 2007, Andy Armstrong C<< <andy@hexten.net> >>.

This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See L<perlartistic>.