FA-3626 / Binary formats / Open access

Packed decimal decodes as a binary integer · case 01

Packed decimal decodes as a binary integer.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Decode one packed BCD byte; reject any nybble above nine with None.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Decode one packed BCD byte; reject any nybble above nine with None.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Decode one packed BCD byte; reject any nybble above nine with None.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve(66), 42)
check('boundary 2', solve(26), None)
check('boundary 3', solve(255), None)
check('boundary 4', solve(0), 0)
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
boundary 1	`66`	`42`	Failed
boundary 2	`26`	`None`	Failed
boundary 3	`255`	`None`	Failed
boundary 4	`0`	`0`	Passed

SHA-256 / 4dbace83473e07c612679ff02e13eff2f03bd795101bb9570caf7d26a26ebb98

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return (x>>4)*10+(x&15)
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve(66), 42)
check('boundary 2', solve(26), None)
check('boundary 3', solve(255), None)
check('boundary 4', solve(0), 0)
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
boundary 1	`42`	`42`	Passed
boundary 2	`20`	`None`	Failed
boundary 3	`165`	`None`	Failed
boundary 4	`0`	`0`	Passed

SHA-256 / 5610b6f8dea49520102624eca4a885c61a6bd4b94983aefe8c755a605f50ed86

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return None if (x>>4)>9 or (x&15)>9 else (x>>4)*10+(x&15)
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve(66), 42)
check('boundary 2', solve(26), None)
check('boundary 3', solve(255), None)
check('boundary 4', solve(0), 0)
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
boundary 1	`42`	`42`	Passed
boundary 2	`None`	`None`	Passed
boundary 3	`None`	`None`	Passed
boundary 4	`0`	`0`	Passed

SHA-256 / 1359dc64314bcd5ca3bedd637c9728867cd62b5af38cca8ad4bf071dadd6bf92

Verification & scope

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 2026-09-29T14:37:28.425211+00:00.

Case digest / 5bfcfe22d59acdc9dafd46f5670f07cbd19a8b3a6f7e64ee84dd9324269d41ad