Table of Contents

Code39Mod43 Class

Definition

Namespace
Bodu.IO.Hashing.CheckDigits
Assembly
Bodu.IO.Hashing.dll
Package
Bodu.IO.Hashing 1.0.0
Source
Code39Mod43.cs

Computes the check character of a Code 39 (also known as Code 3 of 9) symbol string using the modulo 43 scheme. This class cannot be inherited.

public sealed class Code39Mod43 : AlphanumericCheckDigitAlgorithm
Inheritance
Code39Mod43
Inherited Members
Extension Methods

Examples

// Single-call computation against an in-memory body.
char check = Code39Mod43.Compute("CODE39");   // 'W'

// Full-sequence validation.
bool ok = Code39Mod43.IsValid("CODE39W");      // true

// Streaming use when the body is built up incrementally.
var algo = new Code39Mod43();
algo.Append("CODE39");
char d = algo.GetCurrentCheckDigit();          // 'W'

Remarks

The Code 39 modulo-43 check character is the optional self-checking symbol defined by the Code 39 barcode symbology. Each body character is mapped to its ordinal value in the forty-three-symbol Code 39 alphabet - '0'- '9' as 0-9, 'A'-'Z' as 10-35, and the seven symbols '-', '.', space, '$', '/', '+', and '%' as 36-42. The values are summed, reduced modulo 43, and the result is mapped back to the alphabet to produce a single trailing check character.

The scheme detects all single-character substitution errors. Because the underlying combiner is a commutative sum, it does not detect every adjacent transposition; payloads that require transposition coverage should prefer Verhoeff or Damm over a decimal body.

Worked example. For the body "CODE39" the character values are 12, 24, 13, 14, 3, and 9, summing to 75; 75 mod 43 is 32, which maps to 'W'. The resulting string "CODE39W" is therefore valid.

important

This algorithm is not cryptographically secure and should not be used for password hashing, digital signatures, or integrity validation in security-sensitive applications.

Constructors

Code39Mod43()

Initializes a new instance of the Code39Mod43 class.

public Code39Mod43()

Properties

AlgorithmName

Gets the canonical name of the algorithm, suitable for diagnostic output and logging.

public override string AlgorithmName { get; }

Property Value

string

A short, stable identifier such as "Luhn", "IBAN", or "ISO 7064 MOD 97-10".

InputAlphabet

Gets the subset of ASCII from which this algorithm accepts body characters.

public override CheckDigitInputAlphabet InputAlphabet { get; }

Property Value

CheckDigitInputAlphabet

The declared input alphabet.

OutputAlphabet

Gets the subset of ASCII from which this algorithm may emit its check character.

public override CheckDigitOutputAlphabet OutputAlphabet { get; }

Property Value

CheckDigitOutputAlphabet

The declared output alphabet.

Methods

Append(ReadOnlySpan<char>)

Absorbs the supplied characters into the running check-value state.

public override void Append(ReadOnlySpan<char> body)

Parameters

body ReadOnlySpan<char>

The characters to append. Each element must belong to the algorithm's accepted input alphabet. An empty span is a permitted no-op.

Exceptions

ArgumentOutOfRangeException

Thrown when body contains any character outside the algorithm's accepted input alphabet.

Compute(ReadOnlySpan<char>)

Computes the Code 39 modulo-43 check character for the supplied body without allocating a streaming instance.

public static char Compute(ReadOnlySpan<char> body)

Parameters

body ReadOnlySpan<char>

The body characters. Each must belong to the Code 39 alphabet.

Returns

char

The check character drawn from the Code 39 alphabet.

Exceptions

ArgumentOutOfRangeException

Thrown when body contains any character outside the Code 39 alphabet.

GetCurrentCheckDigit()

Returns the check character computed for the body absorbed since the last Reset() (or since construction).

public override char GetCurrentCheckDigit()

Returns

char

The check character as an ASCII character drawn from OutputAlphabet.

Remarks

This call is non-destructive; the running state is unaffected and the method may be invoked any number of times with identical results between appends.

IsValid(ReadOnlySpan<char>)

Determines whether the supplied sequence, comprising a body followed by a trailing Code 39 check character, is consistent.

public static bool IsValid(ReadOnlySpan<char> valueIncludingCheck)

Parameters

valueIncludingCheck ReadOnlySpan<char>

The complete sequence including the trailing check character.

Returns

bool

true if the sequence evaluates as valid under the Code 39 modulo-43 scheme; otherwise, false - including the case where valueIncludingCheck is empty or contains any character outside the Code 39 alphabet.

Reset()

Resets the algorithm to its initial state, discarding any characters previously absorbed.

public override void Reset()

Remarks

Equivalent in behavior to constructing a fresh instance of the same concrete type.

Applies to

ProductVersions
.NET8, 10