FA-79421 / Barcode symbology encoding / Open access

Set C pairs a digit with a following letter · case 01

Data such as "1234567A" produces a set C segment containing "7A".

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The C loop continues while one digit remains, so the pair can include a non-digit.

VERIFIED REPAIR

Stay in C only while at least two digits remain in the run.

Unsuccessful approach: Requiring three digits leaves a final pair in B unnecessarily.

Case contract

Plan Code 128 code sets for printable ASCII data (other characters -> None) as a list of [set, text] segments. Start in C when the data begins with at least 4 digits or is entirely digits of even length >= 2, else B. In C consume digit pairs and fall back to B when fewer than two digits remain in the run. In B switch to C before a run of at least 6 digits, or at least 4 digits that reach the end of the data; an odd run first encodes one digit in B. Empty data yields [["B", ""]].

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.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(data):
    if any(not (32 <= ord(ch) <= 126) for ch in data):
        return None
    n = len(data)
    def run(j):
        k = j
        while k < n and data[k] in '0123456789':
            k += 1
        return k - j
    segs = []
    r = run(0)
    if r >= 4 or (r == n and n >= 2 and n % 2 == 0):
        cur = 'C'
    else:
        cur = 'B'
    buf = ''
    i = 0
    while i < n:
        if cur == 'C':
            if run(i) >= 1:
                buf += data[i:i + 2]
                i += 2
                continue
            segs.append(['C', buf])
            buf = ''
            cur = 'B'
            continue
        r = run(i)
        if r >= 6 or (r >= 4 and i + r == n):
            if r % 2 == 1:
                buf += data[i]
                i += 1
            if buf:
                segs.append(['B', buf])
            buf = ''
            cur = 'C'
            continue
        buf += data[i]
        i += 1
    if buf or not segs:
        segs.append([cur, buf])
    return segs
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['3580131', [['C', '358013'], ['B', '1']]], ['lot17764124x', [['B', 'lot'], ['C', '17764124'], ['B', 'x']]], ['38872Q7088', [['C', '3887'], ['B', '2Q'], ['C', '7088']]], ['xAB', [['B', 'xAB']]], ['AB', [['B', 'AB']]], ['x15', [['B', 'x15']]], ['-', [['B', '-']]], ['83397787832796279-', [['C', '8339778783279627'], ['B', '9-']]]], [['101874486507729', [['C', '10187448650772'], ['B', '9']]], ['82', [['C', '82']]], ['27762 510832', [['C', '2776'], ['B', '2 '], ['C', '510832']]], ['x22', [['B', 'x22']]], [' ', [['B', ' ']]], ['-006', [['B', '-006']]], ['-018', [['B', '-018']]], ['7825577', [['C', '782557'], ['B', '7']]]], [['987793180x', [['C', '98779318'], ['B', '0x']]], ['2921977210', [['C', '2921977210']]], ['99310234894799114-3320', [['C', '9931023489479911'], ['B', '4-'], ['C', '3320']]], ['lot', [['B', 'lot']]], ['1', [['B', '1']]], ['Q7 lotAB', [['B', 'Q7 lotAB']]], ['-00331 ', [['B', '-00331 ']]], ['9912416511515', [['C', '991241651151'], ['B', '5']]]], [['14789849620002739', [['C', '1478984962000273'], ['B', '9']]], ['67847770x7233496217', [['C', '67847770'], ['B', 'x'], ['C', '7233496217']]], ['253922686 -236376801', [['C', '25392268'], ['B', '6 -2'], ['C', '36376801']]], ['lot5899 ', [['B', 'lot5899 ']]], [' Q7', [['B', ' Q7']]], ['-', [['B', '-']]], ['lot', [['B', 'lot']]], ['3807356726022 ', [['C', '380735672602'], ['B', '2 ']]]], [['849552989677181287350031242482230', [['C', '84955298967718128735003124248223'], ['B', '0']]], ['3283655059x2996', [['C', '3283655059'], ['B', 'x'], ['C', '2996']]], ['32998293100126533-08028467', [['C', '3299829310012653'], ['B', '3-'], ['C', '08028467']]], ['x619--', [['B', 'x619--']]], ['113 ', [['B', '113 ']]], [' 10-Q7', [['B', ' 10-Q7']]], ['AB', [['B', 'AB']]], ['5776132lot', [['C', '577613'], ['B', '2lot']]]]]
labels = ["regression: set C exit condition", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: set C exit condition 0	`[['C', '3580131']]`	`[['C', '358013'], ['B', '1']]`	Failed
repair trap 1	`[['B', 'lot'], ['C', '17764124'], ['B', 'x']]`	`[['B', 'lot'], ['C', '17764124'], ['B', 'x']]`	Passed
combined fault 2	`[['C', '38872Q7088']]`	`[['C', '3887'], ['B', '2Q'], ['C', '7088']]`	Failed
control 3	`[['B', 'xAB']]`	`[['B', 'xAB']]`	Passed
control 4	`[['B', 'AB']]`	`[['B', 'AB']]`	Passed
boundary 5	`[['B', 'x15']]`	`[['B', 'x15']]`	Passed
boundary 6	`[['B', '-']]`	`[['B', '-']]`	Passed
control 7	`[['C', '83397787832796279-']]`	`[['C', '8339778783279627'], ['B', '9-']]`	Failed

SHA-256 / 5beb983211e4f071223f00b41b507256889aa003e5bf8eb8509b54573e8c6ba9

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(data):
    if any(not (32 <= ord(ch) <= 126) for ch in data):
        return None
    n = len(data)
    def run(j):
        k = j
        while k < n and data[k] in '0123456789':
            k += 1
        return k - j
    segs = []
    r = run(0)
    if r >= 4 or (r == n and n >= 2 and n % 2 == 0):
        cur = 'C'
    else:
        cur = 'B'
    buf = ''
    i = 0
    while i < n:
        if cur == 'C':
            if run(i) >= 3:
                buf += data[i:i + 2]
                i += 2
                continue
            segs.append(['C', buf])
            buf = ''
            cur = 'B'
            continue
        r = run(i)
        if r >= 6 or (r >= 4 and i + r == n):
            if r % 2 == 1:
                buf += data[i]
                i += 1
            if buf:
                segs.append(['B', buf])
            buf = ''
            cur = 'C'
            continue
        buf += data[i]
        i += 1
    if buf or not segs:
        segs.append([cur, buf])
    return segs
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['3580131', [['C', '358013'], ['B', '1']]], ['lot17764124x', [['B', 'lot'], ['C', '17764124'], ['B', 'x']]], ['38872Q7088', [['C', '3887'], ['B', '2Q'], ['C', '7088']]], ['xAB', [['B', 'xAB']]], ['AB', [['B', 'AB']]], ['x15', [['B', 'x15']]], ['-', [['B', '-']]], ['83397787832796279-', [['C', '8339778783279627'], ['B', '9-']]]], [['101874486507729', [['C', '10187448650772'], ['B', '9']]], ['82', [['C', '82']]], ['27762 510832', [['C', '2776'], ['B', '2 '], ['C', '510832']]], ['x22', [['B', 'x22']]], [' ', [['B', ' ']]], ['-006', [['B', '-006']]], ['-018', [['B', '-018']]], ['7825577', [['C', '782557'], ['B', '7']]]], [['987793180x', [['C', '98779318'], ['B', '0x']]], ['2921977210', [['C', '2921977210']]], ['99310234894799114-3320', [['C', '9931023489479911'], ['B', '4-'], ['C', '3320']]], ['lot', [['B', 'lot']]], ['1', [['B', '1']]], ['Q7 lotAB', [['B', 'Q7 lotAB']]], ['-00331 ', [['B', '-00331 ']]], ['9912416511515', [['C', '991241651151'], ['B', '5']]]], [['14789849620002739', [['C', '1478984962000273'], ['B', '9']]], ['67847770x7233496217', [['C', '67847770'], ['B', 'x'], ['C', '7233496217']]], ['253922686 -236376801', [['C', '25392268'], ['B', '6 -2'], ['C', '36376801']]], ['lot5899 ', [['B', 'lot5899 ']]], [' Q7', [['B', ' Q7']]], ['-', [['B', '-']]], ['lot', [['B', 'lot']]], ['3807356726022 ', [['C', '380735672602'], ['B', '2 ']]]], [['849552989677181287350031242482230', [['C', '84955298967718128735003124248223'], ['B', '0']]], ['3283655059x2996', [['C', '3283655059'], ['B', 'x'], ['C', '2996']]], ['32998293100126533-08028467', [['C', '3299829310012653'], ['B', '3-'], ['C', '08028467']]], ['x619--', [['B', 'x619--']]], ['113 ', [['B', '113 ']]], [' 10-Q7', [['B', ' 10-Q7']]], ['AB', [['B', 'AB']]], ['5776132lot', [['C', '577613'], ['B', '2lot']]]]]
labels = ["regression: set C exit condition", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: set C exit condition 0	`[['C', '358013'], ['B', '1']]`	`[['C', '358013'], ['B', '1']]`	Passed
repair trap 1	`[['B', 'lot'], ['C', '177641'], ['B', '24x']]`	`[['B', 'lot'], ['C', '17764124'], ['B', 'x']]`	Failed
combined fault 2	`[['C', '3887'], ['B', '2Q'], ['C', '70'], ['B', '88']]`	`[['C', '3887'], ['B', '2Q'], ['C', '7088']]`	Failed
control 3	`[['B', 'xAB']]`	`[['B', 'xAB']]`	Passed
control 4	`[['B', 'AB']]`	`[['B', 'AB']]`	Passed
boundary 5	`[['B', 'x15']]`	`[['B', 'x15']]`	Passed
boundary 6	`[['B', '-']]`	`[['B', '-']]`	Passed
control 7	`[['C', '8339778783279627'], ['B', '9-']]`	`[['C', '8339778783279627'], ['B', '9-']]`	Passed

SHA-256 / 7f4ac64d0fd289f60f59b4e7fc363b51e4fdb0af88d2885d4a0b5736f2949c29

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(data):
    if any(not (32 <= ord(ch) <= 126) for ch in data):
        return None
    n = len(data)
    def run(j):
        k = j
        while k < n and data[k] in '0123456789':
            k += 1
        return k - j
    segs = []
    r = run(0)
    if r >= 4 or (r == n and n >= 2 and n % 2 == 0):
        cur = 'C'
    else:
        cur = 'B'
    buf = ''
    i = 0
    while i < n:
        if cur == 'C':
            if run(i) >= 2:
                buf += data[i:i + 2]
                i += 2
                continue
            segs.append(['C', buf])
            buf = ''
            cur = 'B'
            continue
        r = run(i)
        if r >= 6 or (r >= 4 and i + r == n):
            if r % 2 == 1:
                buf += data[i]
                i += 1
            if buf:
                segs.append(['B', buf])
            buf = ''
            cur = 'C'
            continue
        buf += data[i]
        i += 1
    if buf or not segs:
        segs.append([cur, buf])
    return segs
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['3580131', [['C', '358013'], ['B', '1']]], ['lot17764124x', [['B', 'lot'], ['C', '17764124'], ['B', 'x']]], ['38872Q7088', [['C', '3887'], ['B', '2Q'], ['C', '7088']]], ['xAB', [['B', 'xAB']]], ['AB', [['B', 'AB']]], ['x15', [['B', 'x15']]], ['-', [['B', '-']]], ['83397787832796279-', [['C', '8339778783279627'], ['B', '9-']]]], [['101874486507729', [['C', '10187448650772'], ['B', '9']]], ['82', [['C', '82']]], ['27762 510832', [['C', '2776'], ['B', '2 '], ['C', '510832']]], ['x22', [['B', 'x22']]], [' ', [['B', ' ']]], ['-006', [['B', '-006']]], ['-018', [['B', '-018']]], ['7825577', [['C', '782557'], ['B', '7']]]], [['987793180x', [['C', '98779318'], ['B', '0x']]], ['2921977210', [['C', '2921977210']]], ['99310234894799114-3320', [['C', '9931023489479911'], ['B', '4-'], ['C', '3320']]], ['lot', [['B', 'lot']]], ['1', [['B', '1']]], ['Q7 lotAB', [['B', 'Q7 lotAB']]], ['-00331 ', [['B', '-00331 ']]], ['9912416511515', [['C', '991241651151'], ['B', '5']]]], [['14789849620002739', [['C', '1478984962000273'], ['B', '9']]], ['67847770x7233496217', [['C', '67847770'], ['B', 'x'], ['C', '7233496217']]], ['253922686 -236376801', [['C', '25392268'], ['B', '6 -2'], ['C', '36376801']]], ['lot5899 ', [['B', 'lot5899 ']]], [' Q7', [['B', ' Q7']]], ['-', [['B', '-']]], ['lot', [['B', 'lot']]], ['3807356726022 ', [['C', '380735672602'], ['B', '2 ']]]], [['849552989677181287350031242482230', [['C', '84955298967718128735003124248223'], ['B', '0']]], ['3283655059x2996', [['C', '3283655059'], ['B', 'x'], ['C', '2996']]], ['32998293100126533-08028467', [['C', '3299829310012653'], ['B', '3-'], ['C', '08028467']]], ['x619--', [['B', 'x619--']]], ['113 ', [['B', '113 ']]], [' 10-Q7', [['B', ' 10-Q7']]], ['AB', [['B', 'AB']]], ['5776132lot', [['C', '577613'], ['B', '2lot']]]]]
labels = ["regression: set C exit condition", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: set C exit condition 0	`[['C', '358013'], ['B', '1']]`	`[['C', '358013'], ['B', '1']]`	Passed
repair trap 1	`[['B', 'lot'], ['C', '17764124'], ['B', 'x']]`	`[['B', 'lot'], ['C', '17764124'], ['B', 'x']]`	Passed
combined fault 2	`[['C', '3887'], ['B', '2Q'], ['C', '7088']]`	`[['C', '3887'], ['B', '2Q'], ['C', '7088']]`	Passed
control 3	`[['B', 'xAB']]`	`[['B', 'xAB']]`	Passed
control 4	`[['B', 'AB']]`	`[['B', 'AB']]`	Passed
boundary 5	`[['B', 'x15']]`	`[['B', 'x15']]`	Passed
boundary 6	`[['B', '-']]`	`[['B', '-']]`	Passed
control 7	`[['C', '8339778783279627'], ['B', '9-']]`	`[['C', '8339778783279627'], ['B', '9-']]`	Passed

SHA-256 / 15f515ef8e736d0c0f89c1ff3e5585ea59adfbdb4f2332c02d45df25632f5b15

Verification & scope

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.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:44.436411+00:00.

Case digest / bcb2b42c78b160f5d2c9e27b44380d7997ac1a87d2bae3f50d39d23612df5a4e