Implements the Modulo 11 check digit algorithm as defined by FEBRABAN.
Used to validate the general barcode check digit in Brazilian boletos.
Algorithm
- Starting from right to left, multiply each digit by weights 2-9 cyclically
- Sum all products
- Calculate:
11 - (sum mod 11) - Special cases depend on boleto type:
- Banking: 0, 1, 10, 11 → 1
- Convenio: 0, 10, 11 → 0
Summary
Functions
Calculates the Modulo 11 check digit for banking boletos.
Calculates the Modulo 11 check digit for convenio boletos.
Validates that a check digit matches the expected value for banking boletos.
Validates that a check digit matches the expected value for convenio boletos.
Functions
@spec calculate(String.t()) :: non_neg_integer()
Calculates the Modulo 11 check digit for banking boletos.
Maps special cases 0, 1, 10, 11 → 1.
Examples
# All zeros yields sum=0, so 11-(0 mod 11)=11 -> special case returns 1
iex> Brasilex.Boleto.Checksum.Mod11.calculate("0000000000000000000000000000000000000000000")
1@spec calculate_convenio(String.t()) :: non_neg_integer()
Calculates the Modulo 11 check digit for convenio boletos.
Maps special cases 0, 10, 11 → 0 (different from banking).
@spec valid?(String.t(), non_neg_integer() | String.t()) :: boolean()
Validates that a check digit matches the expected value for banking boletos.
Examples
iex> zeros = String.duplicate("0", 43)
iex> Brasilex.Boleto.Checksum.Mod11.valid?(zeros, 1)
true
iex> zeros = String.duplicate("0", 43)
iex> Brasilex.Boleto.Checksum.Mod11.valid?(zeros, "1")
true
iex> zeros = String.duplicate("0", 43)
iex> Brasilex.Boleto.Checksum.Mod11.valid?(zeros, 9)
false@spec valid_convenio?(String.t(), non_neg_integer() | String.t()) :: boolean()
Validates that a check digit matches the expected value for convenio boletos.
Uses convenio variant of Mod11 (maps 0, 10, 11 → 0).