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=head2 EXPORT

C<test_cnpj> is exported by default. C<canon_cnpj>, C<format_cnpj>,
C<parse_cnpj> and C<random_cnpj> can be exported on demand.


=head1 THE CHECK EQUATIONS

A correct CNPJ number has two check digits which are computed
from the 12 first digits. Consider the CNPJ number 
written as 14 digits

  c[1] c[2] c[3] c[4] c[5] c[6] c[7] c[8] c[9] c[10] c[11] c[12] dv[1] dv[2]

To check whether a CNPJ is correct or not, it has to satisfy 
the check equations:

  5*c[1]+4*c[2]+3*c[3]+2*c[4]+9*c[5]+
  8*c[6]+7*c[7]+6*c[8]+5*c[9]+4*c[10]+
                      3*c[11]+2*c[12]+dv[1] = 0 (mod 11) or
                                            = 1 (mod 11) (if dv[1]=0)

and 

  6*c[1]+5*c[2]+4*c[3]+3*c[4]+2*c[5]+
  9*c[6]+8*c[7]+7*c[8]+6*c[9]+5*c[10]+
              4*c[11]+3*c[12]+2*dv[1]+dv[2] = 0 (mod 11) or
                                            = 1 (mod 11) (if dv[2]=0)

=head1 BUGS

I heard that there are exceptions of CNPJ numbers which don't
obey the check equations and are still authentic. I have never found
one of them. 

=head1 SEE ALSO

To make sure this module works, one can try the results obtained against 
those found with  "Emissão de Comprovante de Inscrição e de Situação Cadastral
de Pessoa Jurídica", 
a web page which the Brazilian Ministry of Revenue provides for public 
consultation on regularity status of the taxpayer.
This page tells if the CNPJ number is a correct entry (14-digits-long with verified
check digits), if it references a real company and if it is regular
with the government body. 

Given a bad CNPJ, the after-submit page tells "O número do CNPJ não é válido"
(the CNPJ number is not valid).
If the CNPJ is a good one but does not reference a real company,
it says "CNPJ não existe em nossa base de dados" (CNPJ does not exist
in our database). Otherwise, it shows a details form for the identified
taxpayer.

Note that this module only tests correctness.
It doesn't enter the merit whether the CNPJ number actually exists
at the Brazilian government databases. 

As you might have guessed, this is not the first Perl module
to approach this kind of functionality. Take a look at

  http://search.cpan.org/search?module=Brasil::Checar::CGC

Please reports bugs via CPAN RT, 
http://rt.cpan.org/NoAuth/Bugs.html?Dist=Business-BR-Ids
By doing so, the author will receive your reports and patches, 
as well as the problem and solutions will be documented.

=head1 AUTHOR

A. R. Ferreira, E<lt>ferreira@cpan.orgE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2005 by A. R. Ferreira

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.6 or,
at your option, any later version of Perl 5 you may have available.


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