FAILURE MAP
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FA-79791 / Barcode symbology encoding / Open access

Data Matrix ASCII values are not offset by one · case 01

Every letter decodes as its predecessor in the alphabet.

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

ROOT CAUSE

ASCII characters are written as their code point without the +1 offset.

VERIFIED REPAIR

Write ord(c) + 1.

Unsuccessful approach: Subtracting one shifts in the opposite direction.

Case 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.

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, capacity):
    cw = []
    i = 0
    while i < len(text):
        c = text[i]
        if c in '0123456789' and i + 1 < len(text) and text[i + 1] in '0123456789':
            cw.append(130 + int(text[i:i + 2]))
            i += 2
            continue
        o = ord(c)
        if o > 255:
            return {'error': 'unencodable'}
        if o > 127:
            cw += [235, o - 127]
        else:
            cw.append(o)
        i += 1
    if len(cw) > capacity:
        return {'error': 'overflow'}
    if len(cw) < capacity:
        cw.append(129)
    while len(cw) < capacity:
        p = len(cw) + 1
        v = 129 + ((149 * p) % 253) + 1
        if v > 254:
            v -= 254
        cw.append(v)
    return cw
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('99x', 5), [229, 121, 129, 220, 115]], [('\x800', 7), [235, 1, 49, 129, 115, 11, 161]], [('', 6), [129, 175, 70, 220, 115, 11]], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('\x80', 4), [235, 1, 129, 220]], [('0AB12', 3), {'error': 'overflow'}], [('ABé', 1), {'error': 'overflow'}], [('é99AB0', 10), [235, 106, 229, 66, 67, 49, 129, 56, 206, 101]]], [[(' AB', 4), [33, 66, 67, 129]], [(' x99x', 10), [33, 121, 229, 121, 129, 11, 161, 56, 206, 101]], [('ABxx', 2), {'error': 'overflow'}], [('', 2), [129, 175]], [('x€', 10), {'error': 'unencodable'}], [(' 125', 1), {'error': 'overflow'}], [('99€x', 6), {'error': 'unencodable'}], [('0', 9), [49, 129, 70, 220, 115, 11, 161, 56, 206]]], [[('0', 2), [49, 129]], [('x', 12), [121, 129, 70, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('é€5', 6), {'error': 'unencodable'}], [('éé', 3), {'error': 'overflow'}], [('é\x80\x80', 3), {'error': 'overflow'}], [('', 4), [129, 175, 70, 220]], [('', 5), [129, 175, 70, 220, 115]], [('éÿ5', 9), [235, 106, 235, 128, 54, 129, 161, 56, 206]]], [[('\x80x0', 5), [235, 1, 121, 49, 129]], [('0 ÿ5', 5), [49, 33, 235, 128, 54]], [('', 6), [129, 175, 70, 220, 115, 11]], [('\x8012x5', 1), {'error': 'overflow'}], [(' €ÿ\x80', 5), {'error': 'unencodable'}], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('', 8), [129, 175, 70, 220, 115, 11, 161, 56]], [('0xÿ', 8), [49, 121, 235, 128, 129, 11, 161, 56]]], [[('AB\x805AB', 8), [66, 67, 235, 1, 54, 66, 67, 129]], [('AB', 12), [66, 67, 129, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('990', 1), {'error': 'overflow'}], [('599AB€', 8), {'error': 'unencodable'}], [('', 7), [129, 175, 70, 220, 115, 11, 161]], [('05', 7), [135, 129, 70, 220, 115, 11, 161]], [('\x80€ 0', 8), {'error': 'unencodable'}], [('5', 2), [54, 129]]]]
labels = ["regression: ASCII codeword offset", "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: ASCII codeword offset 0[229, 120, 129, 220, 115][229, 121, 129, 220, 115]Failed
repair trap 1[235, 1, 48, 129, 115, 11, 161][235, 1, 49, 129, 115, 11, 161]Failed
combined fault 2[129, 175, 70, 220, 115, 11][129, 175, 70, 220, 115, 11]Passed
control 3[129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251][129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]Passed
control 4[235, 1, 129, 220][235, 1, 129, 220]Passed
boundary 5{'error': 'overflow'}{'error': 'overflow'}Passed
boundary 6{'error': 'overflow'}{'error': 'overflow'}Passed
control 7[235, 106, 229, 65, 66, 48, 129, 56, 206, 101][235, 106, 229, 66, 67, 49, 129, 56, 206, 101]Failed

SHA-256 / d6d8c6adc32f7fe1b9d9be7092475e8e2fd16eee3b8b2c283cbb8dd8162c0052

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(text, capacity):
    cw = []
    i = 0
    while i < len(text):
        c = text[i]
        if c in '0123456789' and i + 1 < len(text) and text[i + 1] in '0123456789':
            cw.append(130 + int(text[i:i + 2]))
            i += 2
            continue
        o = ord(c)
        if o > 255:
            return {'error': 'unencodable'}
        if o > 127:
            cw += [235, o - 127]
        else:
            cw.append(o - 1)
        i += 1
    if len(cw) > capacity:
        return {'error': 'overflow'}
    if len(cw) < capacity:
        cw.append(129)
    while len(cw) < capacity:
        p = len(cw) + 1
        v = 129 + ((149 * p) % 253) + 1
        if v > 254:
            v -= 254
        cw.append(v)
    return cw
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('99x', 5), [229, 121, 129, 220, 115]], [('\x800', 7), [235, 1, 49, 129, 115, 11, 161]], [('', 6), [129, 175, 70, 220, 115, 11]], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('\x80', 4), [235, 1, 129, 220]], [('0AB12', 3), {'error': 'overflow'}], [('ABé', 1), {'error': 'overflow'}], [('é99AB0', 10), [235, 106, 229, 66, 67, 49, 129, 56, 206, 101]]], [[(' AB', 4), [33, 66, 67, 129]], [(' x99x', 10), [33, 121, 229, 121, 129, 11, 161, 56, 206, 101]], [('ABxx', 2), {'error': 'overflow'}], [('', 2), [129, 175]], [('x€', 10), {'error': 'unencodable'}], [(' 125', 1), {'error': 'overflow'}], [('99€x', 6), {'error': 'unencodable'}], [('0', 9), [49, 129, 70, 220, 115, 11, 161, 56, 206]]], [[('0', 2), [49, 129]], [('x', 12), [121, 129, 70, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('é€5', 6), {'error': 'unencodable'}], [('éé', 3), {'error': 'overflow'}], [('é\x80\x80', 3), {'error': 'overflow'}], [('', 4), [129, 175, 70, 220]], [('', 5), [129, 175, 70, 220, 115]], [('éÿ5', 9), [235, 106, 235, 128, 54, 129, 161, 56, 206]]], [[('\x80x0', 5), [235, 1, 121, 49, 129]], [('0 ÿ5', 5), [49, 33, 235, 128, 54]], [('', 6), [129, 175, 70, 220, 115, 11]], [('\x8012x5', 1), {'error': 'overflow'}], [(' €ÿ\x80', 5), {'error': 'unencodable'}], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('', 8), [129, 175, 70, 220, 115, 11, 161, 56]], [('0xÿ', 8), [49, 121, 235, 128, 129, 11, 161, 56]]], [[('AB\x805AB', 8), [66, 67, 235, 1, 54, 66, 67, 129]], [('AB', 12), [66, 67, 129, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('990', 1), {'error': 'overflow'}], [('599AB€', 8), {'error': 'unencodable'}], [('', 7), [129, 175, 70, 220, 115, 11, 161]], [('05', 7), [135, 129, 70, 220, 115, 11, 161]], [('\x80€ 0', 8), {'error': 'unencodable'}], [('5', 2), [54, 129]]]]
labels = ["regression: ASCII codeword offset", "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: ASCII codeword offset 0[229, 119, 129, 220, 115][229, 121, 129, 220, 115]Failed
repair trap 1[235, 1, 47, 129, 115, 11, 161][235, 1, 49, 129, 115, 11, 161]Failed
combined fault 2[129, 175, 70, 220, 115, 11][129, 175, 70, 220, 115, 11]Passed
control 3[129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251][129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]Passed
control 4[235, 1, 129, 220][235, 1, 129, 220]Passed
boundary 5{'error': 'overflow'}{'error': 'overflow'}Passed
boundary 6{'error': 'overflow'}{'error': 'overflow'}Passed
control 7[235, 106, 229, 64, 65, 47, 129, 56, 206, 101][235, 106, 229, 66, 67, 49, 129, 56, 206, 101]Failed

SHA-256 / 2f94b5dca7f133d4d8a44bbce3794827c3f251a15734d470f279e82ee95d3f57

3 / The verified repair

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

N = 1
observations = []
def solve(text, capacity):
    cw = []
    i = 0
    while i < len(text):
        c = text[i]
        if c in '0123456789' and i + 1 < len(text) and text[i + 1] in '0123456789':
            cw.append(130 + int(text[i:i + 2]))
            i += 2
            continue
        o = ord(c)
        if o > 255:
            return {'error': 'unencodable'}
        if o > 127:
            cw += [235, o - 127]
        else:
            cw.append(o + 1)
        i += 1
    if len(cw) > capacity:
        return {'error': 'overflow'}
    if len(cw) < capacity:
        cw.append(129)
    while len(cw) < capacity:
        p = len(cw) + 1
        v = 129 + ((149 * p) % 253) + 1
        if v > 254:
            v -= 254
        cw.append(v)
    return cw
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('99x', 5), [229, 121, 129, 220, 115]], [('\x800', 7), [235, 1, 49, 129, 115, 11, 161]], [('', 6), [129, 175, 70, 220, 115, 11]], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('\x80', 4), [235, 1, 129, 220]], [('0AB12', 3), {'error': 'overflow'}], [('ABé', 1), {'error': 'overflow'}], [('é99AB0', 10), [235, 106, 229, 66, 67, 49, 129, 56, 206, 101]]], [[(' AB', 4), [33, 66, 67, 129]], [(' x99x', 10), [33, 121, 229, 121, 129, 11, 161, 56, 206, 101]], [('ABxx', 2), {'error': 'overflow'}], [('', 2), [129, 175]], [('x€', 10), {'error': 'unencodable'}], [(' 125', 1), {'error': 'overflow'}], [('99€x', 6), {'error': 'unencodable'}], [('0', 9), [49, 129, 70, 220, 115, 11, 161, 56, 206]]], [[('0', 2), [49, 129]], [('x', 12), [121, 129, 70, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('é€5', 6), {'error': 'unencodable'}], [('éé', 3), {'error': 'overflow'}], [('é\x80\x80', 3), {'error': 'overflow'}], [('', 4), [129, 175, 70, 220]], [('', 5), [129, 175, 70, 220, 115]], [('éÿ5', 9), [235, 106, 235, 128, 54, 129, 161, 56, 206]]], [[('\x80x0', 5), [235, 1, 121, 49, 129]], [('0 ÿ5', 5), [49, 33, 235, 128, 54]], [('', 6), [129, 175, 70, 220, 115, 11]], [('\x8012x5', 1), {'error': 'overflow'}], [(' €ÿ\x80', 5), {'error': 'unencodable'}], [('', 11), [129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]], [('', 8), [129, 175, 70, 220, 115, 11, 161, 56]], [('0xÿ', 8), [49, 121, 235, 128, 129, 11, 161, 56]]], [[('AB\x805AB', 8), [66, 67, 235, 1, 54, 66, 67, 129]], [('AB', 12), [66, 67, 129, 220, 115, 11, 161, 56, 206, 101, 251, 147]], [('990', 1), {'error': 'overflow'}], [('599AB€', 8), {'error': 'unencodable'}], [('', 7), [129, 175, 70, 220, 115, 11, 161]], [('05', 7), [135, 129, 70, 220, 115, 11, 161]], [('\x80€ 0', 8), {'error': 'unencodable'}], [('5', 2), [54, 129]]]]
labels = ["regression: ASCII codeword offset", "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: ASCII codeword offset 0[229, 121, 129, 220, 115][229, 121, 129, 220, 115]Passed
repair trap 1[235, 1, 49, 129, 115, 11, 161][235, 1, 49, 129, 115, 11, 161]Passed
combined fault 2[129, 175, 70, 220, 115, 11][129, 175, 70, 220, 115, 11]Passed
control 3[129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251][129, 175, 70, 220, 115, 11, 161, 56, 206, 101, 251]Passed
control 4[235, 1, 129, 220][235, 1, 129, 220]Passed
boundary 5{'error': 'overflow'}{'error': 'overflow'}Passed
boundary 6{'error': 'overflow'}{'error': 'overflow'}Passed
control 7[235, 106, 229, 66, 67, 49, 129, 56, 206, 101][235, 106, 229, 66, 67, 49, 129, 56, 206, 101]Passed

SHA-256 / c37d26199f3fe267ee226e36eed2159bceb65dbd83af0c52686399e1e0c6f791

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 2026-09-29T14:49:47.652574+00:00.

Case digest / 21bfbdb9985f41de534955099407affdbee7a17e8cfe8a39673d34ad42299d92