FA-79348 / Barcode symbology encoding / Member archive

EAN-13 parity rows for leading digits 7 and 8 are exchanged · case 03

Codes starting with 7 decode as starting with 8 and vice versa, silently changing the country prefix.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Encode a 13-character string of ASCII digits (the check digit is taken as given, not verified) as the 95-module EAN-13 pattern: start guard 101, six left digits in L or G sets chosen by the parity row of the leading digit, centre guard 01010, six right digits in the R set, end guard 101. R is the bitwise complement of L and G is R reversed. Anything else returns None.

Why this case matters

Retail, logistics, pharmacy and document workflows depend on encoders that produce exactly the module pattern, code-set switches, separators and quiet zones scanners expect; one misplaced module or separator makes a label unreadable or, worse, scan as different data.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: parity rows for leading 7 and 8 0	`"10101101110000101011101100111010010001000110101010100111010001001001110101110010111001001000101"`	`"10101101110000101011101100111010111011010011101010100111010001001001110101110010111001001000101"`	Failed

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