FA-79713 / Barcode symbology encoding / Member archive

Pad alternation keyed on codeword position · case 03

Symbols with an odd number of data codewords start padding with 0x11.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Finish a QR data bit stream for a symbol with `capacity` data codewords: data longer than capacity*8 bits returns None; append a terminator of up to four 0 bits (truncated if capacity is reached), pad with 0 bits to a byte boundary, split into codewords, then append pad codewords alternating 0xEC, 0x11 starting with 0xEC until the capacity is filled.

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: pad alternation index 0	`[0, 17, 236]`	`[0, 236, 17]`	Failed

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