FA-79452 / Barcode symbology encoding / Member archive

Leading FNC1 is emitted without a start character · case 02

GS1 symbols begin with value 102 and no start code, so scanners reject them.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Turn planned Code 128 segments into symbol values (without the checksum). Segments are [set, text], ["FNC1"] or ["SHIFT", char]. The first set segment emits its start (A 103, B 104, C 105); later set changes emit Code A 101, Code B 100 or Code C 99. Set A encodes 32..95 as ord-32 and 0..31 as ord+64; set B encodes 32..127 as ord-32; set C encodes even-length ASCII digit text as pair values. FNC1 is 102 and needs a prior start; SHIFT (98) is only valid in A or B and encodes one character in the other of A/B. Errors: no-start, bad-shift, bad-c, unencodable.

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: FNC1 before a start character 0	`[102, 90, 94, 49, 102, 101, 64, 49]`	`{"error": "no-start"}`	Failed

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