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FA-79456 / Barcode symbology encoding / Open access

Code 39 width adds a gap after the stop character · case 01

Label layout reserves one extra narrow module, pushing the symbol into the right quiet zone.

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

ROOT CAUSE

The width adds one intercharacter gap per character instead of one between each adjacent pair.

VERIFIED REPAIR

Add count - 1 gaps.

Unsuccessful approach: Counting gaps only between data characters ignores the gaps next to start and stop.

Case contract

Encode text for Code 39 with a wide:narrow ratio of 2 or 3. Standard mode accepts only the 43 characters 0-9 A-Z - . space $ / + %. Full ASCII mode maps lowercase to "+" plus the capital, controls 1..26 to "$" plus A..Z, NUL to %U, 27..31 to %A..%E, DEL to %T, and punctuation (including the four standard shift characters $ % + /) to its two-character escape. Every symbol character, including the start/stop "*", has 6 narrow and 3 wide elements, and one narrow gap separates adjacent characters. Return the framed data and the total width in narrow modules.

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(text, mode, ratio):
    std = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%'
    if ratio not in (2, 3):
        return {'error': 'ratio'}
    if mode == 'standard':
        for ch in text:
            if ch not in std:
                return {'error': 'char', 'char': ch}
        enc = text
    else:
        punct = {'$': '/D', '%': '/E', '+': '/K', '/': '/O', '!': '/A', '"': '/B', '#': '/C', '&': '/F', "'": '/G',
                 '(': '/H', ')': '/I', '*': '/J', ',': '/L', ':': '/Z', ';': '%F', '<': '%G', '=': '%H', '>': '%I',
                 '?': '%J', '@': '%V', '[': '%K', '\\': '%L', ']': '%M', '^': '%N', '_': '%O', '`': '%W',
                 '{': '%P', '|': '%Q', '}': '%R', '~': '%S'}
        enc = ''
        for ch in text:
            o = ord(ch)
            if o > 127:
                return {'error': 'char', 'char': ch}
            if ch in punct:
                enc += punct[ch]
            elif 'a' <= ch <= 'z':
                enc += '+' + ch.upper()
            elif 1 <= o <= 26:
                enc += '$' + chr(o + 64)
            elif o == 0:
                enc += '%U'
            elif 27 <= o <= 31:
                enc += '%' + chr(o - 27 + 65)
            elif o == 127:
                enc += '%T'
            else:
                enc += ch
    count = len(enc) + 2
    return {'data': '*' + enc + '*', 'modules': count * (6 + 3 * ratio) + count}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('PN/7PN/7$5', 'full', 3), {'data': '*PN/O7PN/O7/D5*', 'modules': 239}], [('', 'standard', 3), {'data': '**', 'modules': 31}], [('café', 'standard', 4), {'error': 'ratio'}], [('ABPN/7PN/7', 'full', 1), {'error': 'ratio'}], [('a+ba+b', 'full', 4), {'error': 'ratio'}], [('Z-9a+blot', 'standard', 2), {'error': 'char', 'char': 'a'}], [('café\t', 'full', 4), {'error': 'ratio'}], [('\x1b', 'full', 2), {'data': '*%A*', 'modules': 51}]], [[('\x1blotlot', 'full', 2), {'data': '*%A+L+O+T+L+O+T*', 'modules': 207}], [('\t\x7fq', 'full', 2), {'data': '*$I%T+Q*', 'modules': 103}], [('', 'standard', 1), {'error': 'ratio'}], [('PN/7\x1blot', 'full', 4), {'error': 'ratio'}], [('\x00caféq', 'full', 4), {'error': 'ratio'}], [('q$5café', 'standard', 4), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('#1', 'full', 2), {'data': '*/C1*', 'modules': 64}]], [[('$5 \x00', 'full', 2), {'data': '*/D5 %U*', 'modules': 103}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'standard', 4), {'error': 'ratio'}], [(' ', 'full', 1), {'error': 'ratio'}], [('*\x1bcafé', 'full', 2), {'error': 'char', 'char': 'é'}], [('', 'full', 4), {'error': 'ratio'}], [('\x7f#1', 'standard', 4), {'error': 'ratio'}], [('ABPN/7Z-9', 'full', 2), {'data': '*ABPN/O7Z-9*', 'modules': 155}]], [[('AB12', 'standard', 2), {'data': '*AB12*', 'modules': 77}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'full', 2), {'error': 'char', 'char': 'é'}], [(' ABPN/7', 'full', 1), {'error': 'ratio'}], [('qAB', 'standard', 3), {'error': 'char', 'char': 'q'}], [('Z-950%', 'full', 1), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('*', 'full', 2), {'data': '*/J*', 'modules': 51}]], [[('$5lot', 'full', 3), {'data': '*/D5+L+O+T*', 'modules': 175}], [('a+ba+b', 'full', 3), {'data': '*+A/K+B+A/K+B*', 'modules': 223}], [('AB\x1b', 'standard', 1), {'error': 'ratio'}], [('Z-9$512', 'standard', 4), {'error': 'ratio'}], [('xq', 'standard', 1), {'error': 'ratio'}], [('\x7f$5', 'full', 1), {'error': 'ratio'}], [('\x7f#1', 'full', 4), {'error': 'ratio'}], [('  \t', 'full', 2), {'data': '*  $I*', 'modules': 77}]]]
labels = ["regression: intercharacter gap count", "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 fixtureActualExpectedOutcome
regression: intercharacter gap count 0{'data': '*PN/O7PN/O7/D5*', 'modules': 240}{'data': '*PN/O7PN/O7/D5*', 'modules': 239}Failed
repair trap 1{'data': '**', 'modules': 32}{'data': '**', 'modules': 31}Failed
combined fault 2{'error': 'ratio'}{'error': 'ratio'}Passed
control 3{'error': 'ratio'}{'error': 'ratio'}Passed
control 4{'error': 'ratio'}{'error': 'ratio'}Passed
boundary 5{'char': 'a', 'error': 'char'}{'char': 'a', 'error': 'char'}Passed
boundary 6{'error': 'ratio'}{'error': 'ratio'}Passed
control 7{'data': '*%A*', 'modules': 52}{'data': '*%A*', 'modules': 51}Failed

SHA-256 / 4ae911225866d58d11fb283207c01df71f68b9c84e789489eeffc9b01aa3978c

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(text, mode, ratio):
    std = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%'
    if ratio not in (2, 3):
        return {'error': 'ratio'}
    if mode == 'standard':
        for ch in text:
            if ch not in std:
                return {'error': 'char', 'char': ch}
        enc = text
    else:
        punct = {'$': '/D', '%': '/E', '+': '/K', '/': '/O', '!': '/A', '"': '/B', '#': '/C', '&': '/F', "'": '/G',
                 '(': '/H', ')': '/I', '*': '/J', ',': '/L', ':': '/Z', ';': '%F', '<': '%G', '=': '%H', '>': '%I',
                 '?': '%J', '@': '%V', '[': '%K', '\\': '%L', ']': '%M', '^': '%N', '_': '%O', '`': '%W',
                 '{': '%P', '|': '%Q', '}': '%R', '~': '%S'}
        enc = ''
        for ch in text:
            o = ord(ch)
            if o > 127:
                return {'error': 'char', 'char': ch}
            if ch in punct:
                enc += punct[ch]
            elif 'a' <= ch <= 'z':
                enc += '+' + ch.upper()
            elif 1 <= o <= 26:
                enc += '$' + chr(o + 64)
            elif o == 0:
                enc += '%U'
            elif 27 <= o <= 31:
                enc += '%' + chr(o - 27 + 65)
            elif o == 127:
                enc += '%T'
            else:
                enc += ch
    count = len(enc) + 2
    return {'data': '*' + enc + '*', 'modules': count * (6 + 3 * ratio) + (count - 2)}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('PN/7PN/7$5', 'full', 3), {'data': '*PN/O7PN/O7/D5*', 'modules': 239}], [('', 'standard', 3), {'data': '**', 'modules': 31}], [('café', 'standard', 4), {'error': 'ratio'}], [('ABPN/7PN/7', 'full', 1), {'error': 'ratio'}], [('a+ba+b', 'full', 4), {'error': 'ratio'}], [('Z-9a+blot', 'standard', 2), {'error': 'char', 'char': 'a'}], [('café\t', 'full', 4), {'error': 'ratio'}], [('\x1b', 'full', 2), {'data': '*%A*', 'modules': 51}]], [[('\x1blotlot', 'full', 2), {'data': '*%A+L+O+T+L+O+T*', 'modules': 207}], [('\t\x7fq', 'full', 2), {'data': '*$I%T+Q*', 'modules': 103}], [('', 'standard', 1), {'error': 'ratio'}], [('PN/7\x1blot', 'full', 4), {'error': 'ratio'}], [('\x00caféq', 'full', 4), {'error': 'ratio'}], [('q$5café', 'standard', 4), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('#1', 'full', 2), {'data': '*/C1*', 'modules': 64}]], [[('$5 \x00', 'full', 2), {'data': '*/D5 %U*', 'modules': 103}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'standard', 4), {'error': 'ratio'}], [(' ', 'full', 1), {'error': 'ratio'}], [('*\x1bcafé', 'full', 2), {'error': 'char', 'char': 'é'}], [('', 'full', 4), {'error': 'ratio'}], [('\x7f#1', 'standard', 4), {'error': 'ratio'}], [('ABPN/7Z-9', 'full', 2), {'data': '*ABPN/O7Z-9*', 'modules': 155}]], [[('AB12', 'standard', 2), {'data': '*AB12*', 'modules': 77}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'full', 2), {'error': 'char', 'char': 'é'}], [(' ABPN/7', 'full', 1), {'error': 'ratio'}], [('qAB', 'standard', 3), {'error': 'char', 'char': 'q'}], [('Z-950%', 'full', 1), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('*', 'full', 2), {'data': '*/J*', 'modules': 51}]], [[('$5lot', 'full', 3), {'data': '*/D5+L+O+T*', 'modules': 175}], [('a+ba+b', 'full', 3), {'data': '*+A/K+B+A/K+B*', 'modules': 223}], [('AB\x1b', 'standard', 1), {'error': 'ratio'}], [('Z-9$512', 'standard', 4), {'error': 'ratio'}], [('xq', 'standard', 1), {'error': 'ratio'}], [('\x7f$5', 'full', 1), {'error': 'ratio'}], [('\x7f#1', 'full', 4), {'error': 'ratio'}], [('  \t', 'full', 2), {'data': '*  $I*', 'modules': 77}]]]
labels = ["regression: intercharacter gap count", "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 fixtureActualExpectedOutcome
regression: intercharacter gap count 0{'data': '*PN/O7PN/O7/D5*', 'modules': 238}{'data': '*PN/O7PN/O7/D5*', 'modules': 239}Failed
repair trap 1{'data': '**', 'modules': 30}{'data': '**', 'modules': 31}Failed
combined fault 2{'error': 'ratio'}{'error': 'ratio'}Passed
control 3{'error': 'ratio'}{'error': 'ratio'}Passed
control 4{'error': 'ratio'}{'error': 'ratio'}Passed
boundary 5{'char': 'a', 'error': 'char'}{'char': 'a', 'error': 'char'}Passed
boundary 6{'error': 'ratio'}{'error': 'ratio'}Passed
control 7{'data': '*%A*', 'modules': 50}{'data': '*%A*', 'modules': 51}Failed

SHA-256 / 08d576bc77d8d667ecdb6f14f70d537020f0ca21f63c28f709c18dbfd79eb605

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(text, mode, ratio):
    std = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%'
    if ratio not in (2, 3):
        return {'error': 'ratio'}
    if mode == 'standard':
        for ch in text:
            if ch not in std:
                return {'error': 'char', 'char': ch}
        enc = text
    else:
        punct = {'$': '/D', '%': '/E', '+': '/K', '/': '/O', '!': '/A', '"': '/B', '#': '/C', '&': '/F', "'": '/G',
                 '(': '/H', ')': '/I', '*': '/J', ',': '/L', ':': '/Z', ';': '%F', '<': '%G', '=': '%H', '>': '%I',
                 '?': '%J', '@': '%V', '[': '%K', '\\': '%L', ']': '%M', '^': '%N', '_': '%O', '`': '%W',
                 '{': '%P', '|': '%Q', '}': '%R', '~': '%S'}
        enc = ''
        for ch in text:
            o = ord(ch)
            if o > 127:
                return {'error': 'char', 'char': ch}
            if ch in punct:
                enc += punct[ch]
            elif 'a' <= ch <= 'z':
                enc += '+' + ch.upper()
            elif 1 <= o <= 26:
                enc += '$' + chr(o + 64)
            elif o == 0:
                enc += '%U'
            elif 27 <= o <= 31:
                enc += '%' + chr(o - 27 + 65)
            elif o == 127:
                enc += '%T'
            else:
                enc += ch
    count = len(enc) + 2
    return {'data': '*' + enc + '*', 'modules': count * (6 + 3 * ratio) + (count - 1)}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('PN/7PN/7$5', 'full', 3), {'data': '*PN/O7PN/O7/D5*', 'modules': 239}], [('', 'standard', 3), {'data': '**', 'modules': 31}], [('café', 'standard', 4), {'error': 'ratio'}], [('ABPN/7PN/7', 'full', 1), {'error': 'ratio'}], [('a+ba+b', 'full', 4), {'error': 'ratio'}], [('Z-9a+blot', 'standard', 2), {'error': 'char', 'char': 'a'}], [('café\t', 'full', 4), {'error': 'ratio'}], [('\x1b', 'full', 2), {'data': '*%A*', 'modules': 51}]], [[('\x1blotlot', 'full', 2), {'data': '*%A+L+O+T+L+O+T*', 'modules': 207}], [('\t\x7fq', 'full', 2), {'data': '*$I%T+Q*', 'modules': 103}], [('', 'standard', 1), {'error': 'ratio'}], [('PN/7\x1blot', 'full', 4), {'error': 'ratio'}], [('\x00caféq', 'full', 4), {'error': 'ratio'}], [('q$5café', 'standard', 4), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('#1', 'full', 2), {'data': '*/C1*', 'modules': 64}]], [[('$5 \x00', 'full', 2), {'data': '*/D5 %U*', 'modules': 103}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'standard', 4), {'error': 'ratio'}], [(' ', 'full', 1), {'error': 'ratio'}], [('*\x1bcafé', 'full', 2), {'error': 'char', 'char': 'é'}], [('', 'full', 4), {'error': 'ratio'}], [('\x7f#1', 'standard', 4), {'error': 'ratio'}], [('ABPN/7Z-9', 'full', 2), {'data': '*ABPN/O7Z-9*', 'modules': 155}]], [[('AB12', 'standard', 2), {'data': '*AB12*', 'modules': 77}], [('', 'full', 2), {'data': '**', 'modules': 25}], [('#1café', 'full', 2), {'error': 'char', 'char': 'é'}], [(' ABPN/7', 'full', 1), {'error': 'ratio'}], [('qAB', 'standard', 3), {'error': 'char', 'char': 'q'}], [('Z-950%', 'full', 1), {'error': 'ratio'}], [('', 'full', 4), {'error': 'ratio'}], [('*', 'full', 2), {'data': '*/J*', 'modules': 51}]], [[('$5lot', 'full', 3), {'data': '*/D5+L+O+T*', 'modules': 175}], [('a+ba+b', 'full', 3), {'data': '*+A/K+B+A/K+B*', 'modules': 223}], [('AB\x1b', 'standard', 1), {'error': 'ratio'}], [('Z-9$512', 'standard', 4), {'error': 'ratio'}], [('xq', 'standard', 1), {'error': 'ratio'}], [('\x7f$5', 'full', 1), {'error': 'ratio'}], [('\x7f#1', 'full', 4), {'error': 'ratio'}], [('  \t', 'full', 2), {'data': '*  $I*', 'modules': 77}]]]
labels = ["regression: intercharacter gap count", "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 fixtureActualExpectedOutcome
regression: intercharacter gap count 0{'data': '*PN/O7PN/O7/D5*', 'modules': 239}{'data': '*PN/O7PN/O7/D5*', 'modules': 239}Passed
repair trap 1{'data': '**', 'modules': 31}{'data': '**', 'modules': 31}Passed
combined fault 2{'error': 'ratio'}{'error': 'ratio'}Passed
control 3{'error': 'ratio'}{'error': 'ratio'}Passed
control 4{'error': 'ratio'}{'error': 'ratio'}Passed
boundary 5{'char': 'a', 'error': 'char'}{'char': 'a', 'error': 'char'}Passed
boundary 6{'error': 'ratio'}{'error': 'ratio'}Passed
control 7{'data': '*%A*', 'modules': 51}{'data': '*%A*', 'modules': 51}Passed

SHA-256 / 1d5e5686d2cd4684a43a08efffd77a0df29045f79d1cbfb1be06ad1497f64cb3

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 2026-09-29T14:49:44.725739+00:00.

Case digest / aa1639f5dd0f7ee64fc244239c50f6e9624a25faac04bc35be488bec7026a3a6