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    my @block = map { $_ & 0xffff_ffff } @{ $block_ref };
    my @key = map { $_ & 0xffff_ffff } @{ $key_ref };
    my $sumation = 0 & 0xffff_ffff;
    my $delta = $DELTA & 0xffff_ffff;
    for my $i ( 0 .. $self->{rounds}-1 ) {
        $sumation = ( $sumation + $delta ) & 0xffff_ffff;
        $block[0] = ( $block[0] + ( ( ( ( ( ( ( ( $block[1] << 4 ) & 0xffff_ffff ) + $key[0] ) & 0xffff_ffff ) ^ ( ( $block[1] + $sumation ) & 0xffff_ffff ) ) & 0xffff_ffff ) ^ ( ( ( ( $block[1] >> 5 ) & 0xffff_ffff ) +  $key[1] ) & 0xffff_ffff ) ) &...
        $block[1] = ( $block[1] + ( ( ( ( ( ( ( ( $block[0] << 4 ) & 0xffff_ffff ) + $key[2] ) & 0xffff_ffff ) ^ ( ( $block[0] + $sumation ) & 0xffff_ffff ) ) & 0xffff_ffff ) ^ ( ( ( ( $block[0] >> 5 ) & 0xffff_ffff ) +  $key[3] ) & 0xffff_ffff ) ) &...
    }
    return \@block;
}

sub decrypt_block {
    my $self = shift;
    my $block_ref = shift;
    my $key_ref = $self->{key};

    croak( sprintf( 'block must has %d elements', $ELEMENTS_IN_BLOCK ) ) if scalar( @{ $block_ref } ) != $ELEMENTS_IN_BLOCK;
    croak( sprintf( 'key must has %d elements', $ELEMENTS_IN_KEY ) ) if scalar( @{ $key_ref } ) != $ELEMENTS_IN_KEY;

    my @block = map { $_ & 0xffff_ffff } @{ $block_ref };
    my @key = map { $_ & 0xffff_ffff } @{ $key_ref };
    my $sumation = $SUMATION & 0xffff_ffff;
    my $delta = $DELTA & 0xffff_ffff;
    for my $i ( 0 .. $self->{rounds}-1 ) {
        $block[1] = ( $block[1] - ( ( ( ( ( ( ( ( $block[0] << 4 ) & 0xffff_ffff ) + $key[2] ) & 0xffff_ffff ) ^ ( ( $block[0] + $sumation ) & 0xffff_ffff ) ) & 0xffff_ffff ) ^ ( ( ( ( $block[0] >> 5 ) & 0xffff_ffff ) + $key[3] ) & 0xffff_ffff ) ) & ...
        $block[0] = ( $block[0] - ( ( ( ( ( ( ( ( $block[1] << 4 ) & 0xffff_ffff ) + $key[0] ) & 0xffff_ffff ) ^ ( ( $block[1] + $sumation ) & 0xffff_ffff ) ) & 0xffff_ffff ) ^ ( ( ( ( $block[1] >> 5 ) & 0xffff_ffff ) + $key[1] ) & 0xffff_ffff ) ) & ...
        $sumation = ( $sumation - $delta ) & 0xffff_ffff;
    }
    return \@block;
}

sub key_setup {
    my $key_str = shift;
    croak( sprintf( 'key must be %s bytes long', $KEY_SIZE ) ) if length( $key_str ) != $KEY_SIZE;
    my @tea_key = unpack 'N*', $key_str;
    return \@tea_key;
}


1;

__END__

=pod

=encoding UTF-8

=head1 NAME

Crypt::TEA_PP - Pure Perl Implementation of the Tiny Encryption Algorithm

=head1 VERSION

version 0.0308

=head1 SYNOPSIS

   use Crypt::TEA_PP;
   use Crypt::CBC;

   my $tea = Crypt::TEA_PP->new( $key );
   my $cbc = Crypt::CBC->new( -cipher => $tea );

   my $text = 'The quick brown fox jumps over the lazy dog.';
   my $cipher_text = $cbc->encrypt( $text );

   my $plain_text = $cbc->decrypt( $cipher_text );

=head1 DESCRIPTION

TEA is a 64-bit symmetric block cipher with a 128-bit key and a variable number of rounds (32 is recommended).
It has a low setup time, and depends on a large number of rounds for security, rather than a complex algorithm.
It was developed by David J. Wheeler and Roger M. Needham,
and is described at L<http://www.ftp.cl.cam.ac.uk/ftp/papers/djw-rmn/djw-rmn-tea.html>

This module implements TEA encryption. It supports the Crypt::CBC interface, with the following functions.

=head1 METHODS

=head2 keysize

Returns the maximum TEA key size, 16 bytes.

=head2 blocksize

Returns the TEA block size, which is 8 bytes. This function exists so that Crypt::TEA_PP can work with Crypt::CBC.

=head2 new

    my $tea = Crypt::TEA_PP->new( $key, $rounds );

This creates a new Crypt::TEA_PP object with the specified key.
The optional rounds parameter specifies the number of rounds of encryption to perform, and defaults to 32.

=head2 encrypt

    $cipher_text = $tea->encrypt($plain_text);

Encrypts blocksize() bytes of $plain_text and returns the corresponding ciphertext.

=head2 decrypt

    $plain_text = $tea->decrypt($cipher_text);

Decrypts blocksize() bytes of $cipher_text and returns the corresponding plaintext.

=head1 SEE ALSO

L<http://www.vader.brad.ac.uk/tea/tea.shtml>

L<Crypt::CBC>

L<Crypt::TEA_XS>

=head1 AUTHOR

Kars Wang <jahiy@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by Kars Wang.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut