Generates fixed-width encode/1 and decode/1 functions in the calling module.

:bits_size sets the exact bit length. :type is :bitstring (default) or :integer; :alphabet accepts an optional custom charlist.

@spec decode_to_bitstring(bitstring(), Keyword.t()) ::
  {:ok, bitstring()} | :error | :error_checksum

Decodes a Crockford Base32 string to a bitstring.

Decoding ignores hyphens and is case-insensitive. Because final zero padding is ambiguous, use a fixed-width encoder when the original bit length must be preserved.

Checksums

With checksum: true, the final non-hyphen symbol is treated as a check symbol and excluded from the payload. A mismatched valid check symbol returns :error_checksum; malformed input returns :error.

Use this option only for values encoded with checksum: true; otherwise the final payload symbol is interpreted as a check symbol.

Examples

iex> CrockfordBase32.decode_to_bitstring("C5H66")
{:ok, "abc"}
iex> CrockfordBase32.decode_to_bitstring("C5H-66C", checksum: true)
{:ok, "abc"}
iex> CrockfordBase32.decode_to_bitstring("C5H66D", checksum: true)
:error_checksum

@spec decode_to_integer(String.t(), Keyword.t()) ::
  {:ok, non_neg_integer()} | :error | :error_checksum

Decodes a Crockford Base32 string to a non-negative integer.

Decoding ignores hyphens and is case-insensitive. I and L are aliases for 1, and O is an alias for 0.

Checksums

With checksum: true, the final non-hyphen symbol is treated as a check symbol and excluded from the payload. A mismatched valid check symbol returns :error_checksum; malformed input returns :error.

Use this option only for values encoded with checksum: true; otherwise the final payload symbol is interpreted as a check symbol.

Examples

iex> CrockfordBase32.decode_to_integer("16-j")
{:ok, 1234}
iex> CrockfordBase32.decode_to_integer("16-JD", checksum: true)
{:ok, 1234}
iex> CrockfordBase32.decode_to_integer("16J1", checksum: true)
:error_checksum

@spec encode(non_neg_integer() | bitstring(), Keyword.t()) :: String.t()

Encodes a non-negative integer or bitstring.

Bitstrings may have any bit length. Output uses the default Crockford alphabet, "0123456789ABCDEFGHJKMNPQRSTVWXYZ".

Checksums

Setting checksum: true appends one Crockford check symbol after the payload. The symbol is calculated modulo 37; for bitstrings, the calculation uses the original, unpadded bits. It helps detect accidental transcription errors, but is not a cryptographic integrity or authentication mechanism.

Check symbols extend the output alphabet with "*~$=U". split_size is applied after the check symbol is appended, so it is grouped with the rest of the output.

Options

• :checksum - set to true to append a check symbol.
• :split_size - a positive group size; groups are separated by hyphens.

Examples

iex> CrockfordBase32.encode(1234)
"16J"
iex> CrockfordBase32.encode(1234, checksum: true)
"16JD"
iex> CrockfordBase32.encode("abc", checksum: true, split_size: 3)
"C5H-66C"