FA-79352 / Barcode symbology encoding / Member archive

EAN-13 left half encodes the implied leading digit · case 02

The encoded symbol repeats the first digit and drops the seventh.

Member previewVariant 2 · 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: left half digit index 0	`"10100011010111011011101101110110110111010111101010100010011100101001110110011010001001101100101"`	`"10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101"`	Failed

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