Hawkynt

Constant Weight Code

Error detection code where all valid codewords have the same Hamming weight (m-of-n codes). Can detect all unidirectional errors by verifying constant number of 1-bits. Used in balanced transmission and self-checking circuits.

Properties

Property	Value
Category	Checksums
Sub-category	Unidirectional Error Detection
Security status	🎓 Educational Only
Complexity	Beginner
Inventor	Unknown (Coding Theory Concept)
Year	1960
Origin	Not specified
Source	algorithms/checksum/constant-weight.js

Security

Status: 🎓 Educational Only

Known vulnerabilities

Issue	Description	Mitigation
No Error Correction	Constant weight codes can only detect errors, not correct them (basic variant).	—
Limited Code Space	Only C(n,m) valid codewords exist, limiting information capacity.	—

Notes

• Result() returns the codeword unchanged; this class checks a codeword, it does not encode one.
• A weight violation is only reported on the console, so callers cannot act on it - use DetectError() instead, which does return a verdict.
• Because Result() carries no verdict, an invalid codeword cannot be expressed as a test vector.

Documentation

• Wikipedia - Constant Weight Code
• Error Correction Zoo
• IEEE Paper on CW Codes

References

• Single Error Correction
• Classification of CW Codes

Test vectors

4 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — 3-of-5 codeword with weight 3 (0 1 0 1 1)

Field	Value
weight	3
length	5
input	0001000101
expected	0001000101

Vector 2 — 3-of-5 codeword with weight 3 (1 1 1 0 0)

Field	Value
weight	3
length	5
input	0101010000
expected	0101010000

Vector 3 — 2-of-4 codeword with weight 2 (1 0 1 0)

Field	Value
weight	2
length	4
input	01000100
expected	01000100

Vector 4 — 2-of-4 codeword with weight 2 (0 1 0 1)

Field	Value
weight	2
length	4
input	00010001
expected	00010001

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