{"abstract":"Format words disagree with printed symbols; decoding finds nothing within distance 3.","category":"Error-correcting codes","checks":8,"contract":"QR code format information, a BCH(15,5) code. \"encode\" takes [level, mask] with level bits L=01, M=00, Q=11, H=10 and mask 0..7 (else None): data = level<<3 | mask, append the 10-bit remainder of data*x^10 modulo 0x537, then XOR 0x5412. \"decode\" takes a 15-bit integer and returns [level, mask, distance] for the unique format word within Hamming distance 3, else None.","contract_signature":"op, x","evaluation_group":"w2-error_correcting_codes-qr-format-info","failed_approach":"Masking only the five data bits before computing the remainder yields a different codeword.","family":"w2-error_correcting_codes-qr-format-info-mask-xor","id":"FA-72161","implementations":{"attempt":{"sha256":"8aa8d052019da3e2dc93cd2616bbc9e58337301f77703177086d5d1b24c0a9c0","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(op, x):\n    EC = {'L': 1, 'M': 0, 'Q': 3, 'H': 2}\n    def enc(level, mask):\n        data = ((EC[level] << 3) | mask) ^ 0b10101\n        rem = data << 10\n        for i in range(14, 9, -1):\n            if rem & (1 << i):\n                rem ^= 0x537 << (i - 10)\n        return (data << 10) | rem\n    if op == 'encode':\n        level, mask = x\n        if level not in EC or not 0 <= mask <= 7:\n            return None\n        return enc(level, mask)\n    best = None\n    for level in 'LMQH':\n        for mask in range(8):\n            dist = bin(enc(level, mask) ^ x).count('1')\n            if dist <= 3 and (best is None or dist < best[2]):\n                best = [level, mask, dist]\n    return best\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[['regression [\"encode\", [\"L\", 0]]', ['encode', ['L', 0]], 30660], ['regression [\"encode\", [\"L\", 3]]', ['encode', ['L', 3]], 30877], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"L\", 7]]', ['encode', ['L', 7]], 26998], ['control [\"encode\", [\"M\", 0]]', ['encode', ['M', 0]], 21522], ['control [\"encode\", [\"M\", 3]]', ['encode', ['M', 3]], 23371]], [['regression [\"encode\", [\"L\", 7]]', ['encode', ['L', 7]], 26998], ['regression [\"encode\", [\"M\", 0]]', ['encode', ['M', 0]], 21522], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"encode\", [\"Q\", 0]]', ['encode', ['Q', 0]], 13663], ['control [\"encode\", [\"Q\", 3]]', ['encode', ['Q', 3]], 14854], ['control [\"encode\", [\"Q\", 5]]', ['encode', ['Q', 5]], 8579]], [['regression [\"encode\", [\"M\", 5]]', ['encode', ['M', 5]], 16590], ['regression [\"encode\", [\"M\", 7]]', ['encode', ['M', 7]], 19104], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"H\", 3]]', ['encode', ['H', 3]], 6608], ['control [\"encode\", [\"H\", 5]]', ['encode', ['H', 5]], 597], ['control [\"encode\", [\"H\", 7]]', ['encode', ['H', 7]], 2107]], [['regression [\"encode\", [\"Q\", 3]]', ['encode', ['Q', 3]], 14854], ['regression [\"encode\", [\"Q\", 5]]', ['encode', ['Q', 5]], 8579], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"decode\", 19724]', ['decode', 19724], ['H', 6, 1]], ['control [\"decode\", 6616]', ['decode', 6616], ['H', 3, 1]], ['control [\"decode\", 20345]', ['decode', 20345], ['M', 4, 3]]], [['regression [\"encode\", [\"H\", 0]]', ['encode', ['H', 0]], 5769], ['regression [\"encode\", [\"H\", 3]]', ['encode', ['H', 3]], 6608], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 2309]', ['decode', 2309], ['H', 6, 3]], ['control [\"decode\", 2099]', ['decode', 2099], ['H', 7, 1]], ['control [\"decode\", 27094]', ['decode', 27094], ['L', 7, 2]]]]\nfor label, args, expected in fixtures[N - 1]:\n    check(label, 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":"c371a5c11e56894ef2df6bce33b07dc575286a86e48de2e3361cbd0a52966f42","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(op, x):\n    EC = {'L': 1, 'M': 0, 'Q': 3, 'H': 2}\n    def enc(level, mask):\n        data = (EC[level] << 3) | mask\n        rem = data << 10\n        for i in range(14, 9, -1):\n            if rem & (1 << i):\n                rem ^= 0x537 << (i - 10)\n        return (data << 10) | rem\n    if op == 'encode':\n        level, mask = x\n        if level not in EC or not 0 <= mask <= 7:\n            return None\n        return enc(level, mask)\n    best = None\n    for level in 'LMQH':\n        for mask in range(8):\n            dist = bin(enc(level, mask) ^ x).count('1')\n            if dist <= 3 and (best is None or dist < best[2]):\n                best = [level, mask, dist]\n    return best\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[['regression [\"encode\", [\"L\", 0]]', ['encode', ['L', 0]], 30660], ['regression [\"encode\", [\"L\", 3]]', ['encode', ['L', 3]], 30877], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"L\", 7]]', ['encode', ['L', 7]], 26998], ['control [\"encode\", [\"M\", 0]]', ['encode', ['M', 0]], 21522], ['control [\"encode\", [\"M\", 3]]', ['encode', ['M', 3]], 23371]], [['regression [\"encode\", [\"L\", 7]]', ['encode', ['L', 7]], 26998], ['regression [\"encode\", [\"M\", 0]]', ['encode', ['M', 0]], 21522], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"encode\", [\"Q\", 0]]', ['encode', ['Q', 0]], 13663], ['control [\"encode\", [\"Q\", 3]]', ['encode', ['Q', 3]], 14854], ['control [\"encode\", [\"Q\", 5]]', ['encode', ['Q', 5]], 8579]], [['regression [\"encode\", [\"M\", 5]]', ['encode', ['M', 5]], 16590], ['regression [\"encode\", [\"M\", 7]]', ['encode', ['M', 7]], 19104], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"H\", 3]]', ['encode', ['H', 3]], 6608], ['control [\"encode\", [\"H\", 5]]', ['encode', ['H', 5]], 597], ['control [\"encode\", [\"H\", 7]]', ['encode', ['H', 7]], 2107]], [['regression [\"encode\", [\"Q\", 3]]', ['encode', ['Q', 3]], 14854], ['regression [\"encode\", [\"Q\", 5]]', ['encode', ['Q', 5]], 8579], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"decode\", 19724]', ['decode', 19724], ['H', 6, 1]], ['control [\"decode\", 6616]', ['decode', 6616], ['H', 3, 1]], ['control [\"decode\", 20345]', ['decode', 20345], ['M', 4, 3]]], [['regression [\"encode\", [\"H\", 0]]', ['encode', ['H', 0]], 5769], ['regression [\"encode\", [\"H\", 3]]', ['encode', ['H', 3]], 6608], ['control [\"decode\", 21533]', ['decode', 21533], None], ['control [\"encode\", [\"X\", 1]]', ['encode', ['X', 1]], None], ['control [\"encode\", [\"L\", 8]]', ['encode', ['L', 8]], None], ['control [\"decode\", 2309]', ['decode', 2309], ['H', 6, 3]], ['control [\"decode\", 2099]', ['decode', 2099], ['H', 7, 1]], ['control [\"decode\", 27094]', ['decode', 27094], ['L', 7, 2]]]]\nfor label, args, expected in fixtures[N - 1]:\n    check(label, 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 of the named code under the stated contract; not a production codec. 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-error_correcting_codes-qr-format-info-mask-xor","generated_at":"2026-09-29T14:48:36.037070+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"QR readers must recover the error-correction level and mask pattern before decoding any data module.","root_cause":"The BCH codeword is returned without XORing the fixed mask 0x5412.","sha256":"4ad7f3070778f929431ef2285e1788c1a566346a58ad85170fede7cf4c348bc9","title":"QR format encoder omits the 0x5412 mask · 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":39.751,"exit_code":1,"observations":[{"actual":30097,"check":"regression [\"encode\", [\"L\", 0]]","expected":30660,"passed":false},{"actual":31432,"check":"regression [\"encode\", [\"L\", 3]]","expected":30877,"passed":false},{"actual":null,"check":"control [\"encode\", [\"X\", 1]]","expected":null,"passed":true},{"actual":null,"check":"control [\"encode\", [\"L\", 8]]","expected":null,"passed":true},{"actual":null,"check":"control [\"decode\", 21533]","expected":null,"passed":true},{"actual":27427,"check":"control [\"encode\", [\"L\", 7]]","expected":26998,"passed":false},{"actual":22087,"check":"control [\"encode\", [\"M\", 0]]","expected":21522,"passed":false},{"actual":22814,"check":"control [\"encode\", [\"M\", 3]]","expected":23371,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression [\\\"encode\\\", [\\\"L\\\", 0]]\", \"actual\": 30097, \"expected\": 30660, \"passed\": false}, {\"check\": \"regression [\\\"encode\\\", [\\\"L\\\", 3]]\", \"actual\": 31432, \"expected\": 30877, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"X\\\", 1]]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"encode\\\", [\\\"L\\\", 8]]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"decode\\\", 21533]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"encode\\\", [\\\"L\\\", 7]]\", \"actual\": 27427, \"expected\": 26998, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"M\\\", 0]]\", \"actual\": 22087, \"expected\": 21522, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"M\\\", 3]]\", \"actual\": 22814, \"expected\": 23371, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":39.164,"exit_code":1,"observations":[{"actual":9174,"check":"regression [\"encode\", [\"L\", 0]]","expected":30660,"passed":false},{"actual":11407,"check":"regression [\"encode\", [\"L\", 3]]","expected":30877,"passed":false},{"actual":null,"check":"control [\"encode\", [\"X\", 1]]","expected":null,"passed":true},{"actual":null,"check":"control [\"encode\", [\"L\", 8]]","expected":null,"passed":true},{"actual":null,"check":"control [\"decode\", 21533]","expected":null,"passed":true},{"actual":15716,"check":"control [\"encode\", [\"L\", 7]]","expected":26998,"passed":false},{"actual":0,"check":"control [\"encode\", [\"M\", 0]]","expected":21522,"passed":false},{"actual":3929,"check":"control [\"encode\", [\"M\", 3]]","expected":23371,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression [\\\"encode\\\", [\\\"L\\\", 0]]\", \"actual\": 9174, \"expected\": 30660, \"passed\": false}, {\"check\": \"regression [\\\"encode\\\", [\\\"L\\\", 3]]\", \"actual\": 11407, \"expected\": 30877, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"X\\\", 1]]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"encode\\\", [\\\"L\\\", 8]]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"decode\\\", 21533]\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"control [\\\"encode\\\", [\\\"L\\\", 7]]\", \"actual\": 15716, \"expected\": 26998, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"M\\\", 0]]\", \"actual\": 0, \"expected\": 21522, \"passed\": false}, {\"check\": \"control [\\\"encode\\\", [\\\"M\\\", 3]]\", \"actual\": 3929, \"expected\": 23371, \"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."}}