{"abstract":"Decoders do not recognise the end of data because the first pad is not 129.","category":"Barcode symbology encoding","checks":8,"contract":"Data Matrix ASCII encodation into `capacity` data codewords: two consecutive ASCII digits become 130 + their value; ASCII 0..127 becomes ord + 1; 128..255 becomes Upper Shift 235 then ord - 127; higher code points are unencodable. Too many codewords -> overflow. Padding: the first pad is 129; each later pad at 1-based position p is 129 + ((149 * p) mod 253) + 1, minus 254 if above 254.","contract_signature":"text, capacity","evaluation_group":"w2-barcode-symbology-encoding-datamatrix-ascii","failed_approach":"128 is an ASCII codeword, not the pad value.","family":"w2-barcode-symbology-encoding-datamatrix-ascii-first-pad","id":"FA-79806","implementations":{"attempt":{"sha256":"b7dd372edc2191c93767fd2eb81f01716f3b16a7bc9ad0cbb323f0ce6ee7252a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(text, capacity):\n    cw = []\n    i = 0\n    while i < len(text):\n        c = text[i]\n        if c in '0123456789' and i + 1 < len(text) and text[i + 1] in '0123456789':\n            cw.append(130 + int(text[i:i + 2]))\n            i += 2\n            continue\n        o = ord(c)\n        if o > 255:\n            return {'error': 'unencodable'}\n        if o > 127:\n            cw += [235, o - 127]\n        else:\n            cw.append(o + 1)\n        i += 1\n    if len(cw) > capacity:\n        return {'error': 'overflow'}\n    if len(cw) < capacity:\n        cw.append(128)\n    while len(cw) < capacity:\n        p = len(cw) + 1\n        v = 129 + ((149 * p) % 253) + 1\n        if v > 254:\n            v -= 254\n        cw.append(v)\n    return cw\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[[('', 6), [129, 175, 70, 220, 115, 11]], [('\\x80', 4), [235, 1, 129, 220]], [('0AB12', 3), {'error': 'overflow'}], [('ABé', 1), {'error': 'overflow'}], [('AB€€', 10), {'error': 'unencodable'}], [(' ÿ5', 2), {'error': 'overflow'}], [('é \\x80AB', 4), {'error': 'overflow'}], [('99x', 5), [229, 121, 129, 220, 115]]], [[(' ABAB12', 8), [33, 66, 67, 66, 67, 142, 129, 56]], [('x', 4), [121, 129, 70, 220]], [('x€', 10), {'error': 'unencodable'}], [(' 125', 1), {'error': 'overflow'}], [('99€x', 6), {'error': 'unencodable'}], [('ÿ€', 10), {'error': 'unencodable'}], [(' €5', 5), {'error': 'unencodable'}], [(' AB', 4), [33, 66, 67, 129]]], [[('', 4), [129, 175, 70, 220]], [('99é0', 5), [229, 235, 106, 49, 129]], [('éé', 3), {'error': 'overflow'}], [('é\\x80\\x80', 3), {'error': 'overflow'}], [('€', 6), {'error': 'unencodable'}], [('xAB99', 2), {'error': 'overflow'}], [('12é\\x80', 1), {'error': 'overflow'}], [('x99AB', 11), [121, 229, 66, 67, 129, 11, 161, 56, 206, 101, 251]]], [[('0xÿ', 8), [49, 121, 235, 128, 129, 11, 161, 56]], [('99', 3), [229, 129, 70]], [('\\x8012x5', 1), {'error': 'overflow'}], [(' €ÿ\\x80', 5), {'error': 'unencodable'}], [('AB€x', 2), {'error': 'unencodable'}], [('€ ', 4), {'error': 'unencodable'}], [('€', 2), {'error': 'unencodable'}], [('', 6), [129, 175, 70, 220, 115, 11]]], [[('', 7), [129, 175, 70, 220, 115, 11, 161]], [('xÿ99', 9), [121, 235, 128, 229, 129, 11, 161, 56, 206]], [('\\x80€ 0', 8), {'error': 'unencodable'}], [('€99', 7), {'error': 'unencodable'}], [('€\\x80', 9), {'error': 'unencodable'}], [('\\x80', 1), {'error': 'overflow'}], [('AB€x', 3), {'error': 'unencodable'}], [(' 12\\x80x', 7), [33, 142, 235, 1, 121, 129, 161]]]]\nlabels = [\"regression: first pad codeword\", \"repair trap\", \"combined fault\", \"control\", \"control\", \"boundary\", \"boundary\", \"control\"]\nfor i, (args, expected) in enumerate(fixtures[N-1]):\n    check(\"%s %d\" % (labels[i % len(labels)], i), solve(*args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"c36da54839c7abb847f010566838f485213e1e5e1d23caa81b48a4f8bc6b8884","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(text, capacity):\n    cw = []\n    i = 0\n    while i < len(text):\n        c = text[i]\n        if c in '0123456789' and i + 1 < len(text) and text[i + 1] in '0123456789':\n            cw.append(130 + int(text[i:i + 2]))\n            i += 2\n            continue\n        o = ord(c)\n        if o > 255:\n            return {'error': 'unencodable'}\n        if o > 127:\n            cw += [235, o - 127]\n        else:\n            cw.append(o + 1)\n        i += 1\n    if len(cw) > capacity:\n        return {'error': 'overflow'}\n    while len(cw) < capacity:\n        p = len(cw) + 1\n        v = 129 + ((149 * p) % 253) + 1\n        if v > 254:\n            v -= 254\n        cw.append(v)\n    return cw\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[[('', 6), [129, 175, 70, 220, 115, 11]], [('\\x80', 4), [235, 1, 129, 220]], [('0AB12', 3), {'error': 'overflow'}], [('ABé', 1), {'error': 'overflow'}], [('AB€€', 10), {'error': 'unencodable'}], [(' ÿ5', 2), {'error': 'overflow'}], [('é \\x80AB', 4), {'error': 'overflow'}], [('99x', 5), [229, 121, 129, 220, 115]]], [[(' ABAB12', 8), [33, 66, 67, 66, 67, 142, 129, 56]], [('x', 4), [121, 129, 70, 220]], [('x€', 10), {'error': 'unencodable'}], [(' 125', 1), {'error': 'overflow'}], [('99€x', 6), {'error': 'unencodable'}], [('ÿ€', 10), {'error': 'unencodable'}], [(' €5', 5), {'error': 'unencodable'}], [(' AB', 4), [33, 66, 67, 129]]], [[('', 4), [129, 175, 70, 220]], [('99é0', 5), [229, 235, 106, 49, 129]], [('éé', 3), {'error': 'overflow'}], [('é\\x80\\x80', 3), {'error': 'overflow'}], [('€', 6), {'error': 'unencodable'}], [('xAB99', 2), {'error': 'overflow'}], [('12é\\x80', 1), {'error': 'overflow'}], [('x99AB', 11), [121, 229, 66, 67, 129, 11, 161, 56, 206, 101, 251]]], [[('0xÿ', 8), [49, 121, 235, 128, 129, 11, 161, 56]], [('99', 3), [229, 129, 70]], [('\\x8012x5', 1), {'error': 'overflow'}], [(' €ÿ\\x80', 5), {'error': 'unencodable'}], [('AB€x', 2), {'error': 'unencodable'}], [('€ ', 4), {'error': 'unencodable'}], [('€', 2), {'error': 'unencodable'}], [('', 6), [129, 175, 70, 220, 115, 11]]], [[('', 7), [129, 175, 70, 220, 115, 11, 161]], [('xÿ99', 9), [121, 235, 128, 229, 129, 11, 161, 56, 206]], [('\\x80€ 0', 8), {'error': 'unencodable'}], [('€99', 7), {'error': 'unencodable'}], [('€\\x80', 9), {'error': 'unencodable'}], [('\\x80', 1), {'error': 'overflow'}], [('AB€x', 3), {'error': 'unencodable'}], [(' 12\\x80x', 7), [33, 142, 235, 1, 121, 129, 161]]]]\nlabels = [\"regression: first pad codeword\", \"repair trap\", \"combined fault\", \"control\", \"control\", \"boundary\", \"boundary\", \"control\"]\nfor i, (args, expected) in enumerate(fixtures[N-1]):\n    check(\"%s %d\" % (labels[i % len(labels)], i), solve(*args), expected)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"A deterministic bounded teaching model with a stipulated contract; it makes no claim of conformance to any published specification. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"w2-barcode-symbology-encoding-datamatrix-ascii-first-pad","generated_at":"2026-09-29T14:49:47.893367+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"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.","root_cause":"Every pad is randomised, including the first one that must be the literal 129.","sha256":"250944c19ab7ee2c00b96d6e52d9edf3d046b0c122a11674fb15d21c0a7e365f","title":"First pad codeword is randomised · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":41.766,"exit_code":1,"observations":[{"actual":[128,175,70,220,115,11],"check":"regression: first pad codeword 0","expected":[129,175,70,220,115,11],"passed":false},{"actual":[235,1,128,220],"check":"repair trap 1","expected":[235,1,129,220],"passed":false},{"actual":{"error":"overflow"},"check":"combined fault 2","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"overflow"},"check":"control 3","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"unencodable"},"check":"control 4","expected":{"error":"unencodable"},"passed":true},{"actual":{"error":"overflow"},"check":"boundary 5","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"overflow"},"check":"boundary 6","expected":{"error":"overflow"},"passed":true},{"actual":[229,121,128,220,115],"check":"control 7","expected":[229,121,129,220,115],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression: first pad codeword 0\", \"actual\": [128, 175, 70, 220, 115, 11], \"expected\": [129, 175, 70, 220, 115, 11], \"passed\": false}, {\"check\": \"repair trap 1\", \"actual\": [235, 1, 128, 220], \"expected\": [235, 1, 129, 220], \"passed\": false}, {\"check\": \"combined fault 2\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 3\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 4\", \"actual\": {\"error\": \"unencodable\"}, \"expected\": {\"error\": \"unencodable\"}, \"passed\": true}, {\"check\": \"boundary 5\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"boundary 6\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 7\", \"actual\": [229, 121, 128, 220, 115], \"expected\": [229, 121, 129, 220, 115], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.153,"exit_code":1,"observations":[{"actual":[25,175,70,220,115,11],"check":"regression: first pad codeword 0","expected":[129,175,70,220,115,11],"passed":false},{"actual":[235,1,70,220],"check":"repair trap 1","expected":[235,1,129,220],"passed":false},{"actual":{"error":"overflow"},"check":"combined fault 2","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"overflow"},"check":"control 3","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"unencodable"},"check":"control 4","expected":{"error":"unencodable"},"passed":true},{"actual":{"error":"overflow"},"check":"boundary 5","expected":{"error":"overflow"},"passed":true},{"actual":{"error":"overflow"},"check":"boundary 6","expected":{"error":"overflow"},"passed":true},{"actual":[229,121,70,220,115],"check":"control 7","expected":[229,121,129,220,115],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression: first pad codeword 0\", \"actual\": [25, 175, 70, 220, 115, 11], \"expected\": [129, 175, 70, 220, 115, 11], \"passed\": false}, {\"check\": \"repair trap 1\", \"actual\": [235, 1, 70, 220], \"expected\": [235, 1, 129, 220], \"passed\": false}, {\"check\": \"combined fault 2\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 3\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 4\", \"actual\": {\"error\": \"unencodable\"}, \"expected\": {\"error\": \"unencodable\"}, \"passed\": true}, {\"check\": \"boundary 5\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"boundary 6\", \"actual\": {\"error\": \"overflow\"}, \"expected\": {\"error\": \"overflow\"}, \"passed\": true}, {\"check\": \"control 7\", \"actual\": [229, 121, 70, 220, 115], \"expected\": [229, 121, 129, 220, 115], \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}