FA-3611 / Binary formats / Open access

A signed octet is interpreted as an unsigned magnitude · case 01

A signed octet is interpreted as an unsigned magnitude.

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 octet as signed two-complement.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Decode one octet as signed two-complement.

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

Case contract

Decode one octet as signed two-complement.

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(255), -1)
check('boundary 2', solve(128), -128)
check('boundary 3', solve(127), 127)
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	`255`	`-1`	Failed
boundary 2	`128`	`-128`	Failed
boundary 3	`127`	`127`	Passed
boundary 4	`0`	`0`	Passed

SHA-256 / 2c739ff62280c0cfedbe27129640a67eadcad4865376d0ae645c5d6e5a81c3a8

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-128 if x>=128 else 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(255), -1)
check('boundary 2', solve(128), -128)
check('boundary 3', solve(127), 127)
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	`127`	`-1`	Failed
boundary 2	`0`	`-128`	Failed
boundary 3	`127`	`127`	Passed
boundary 4	`0`	`0`	Passed

SHA-256 / 4055920f3a66d7e1088c3d51a3b60a629eccd711a69028f5cef524004df102b7

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 x-256 if x>=128 else 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(255), -1)
check('boundary 2', solve(128), -128)
check('boundary 3', solve(127), 127)
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	`-1`	`-1`	Passed
boundary 2	`-128`	`-128`	Passed
boundary 3	`127`	`127`	Passed
boundary 4	`0`	`0`	Passed

SHA-256 / 26a108c0dc936942b06f0bc273c2d9f3772422dce632bfb9bce02092563baae9

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 2026-09-29T14:37:28.378065+00:00.

Case digest / 13d2ad1678910676e0ec28d682261d092778600fe77ee2634ac34599d0a02591