FA-49771 / PCM sample encoding / Open access

Pcm nibble block order: high mask · case 01

Transport bits above the octet leak into the high nibble.

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

ROOT CAUSE

Transport bits above the octet leak into the high nibble.

VERIFIED REPAIR

Use the stated conversion contract at high mask.

Unsuccessful approach: Reusing low nibble duplicates the second sample code.

Case contract

Extract adaptive PCM nibble codes in declared within-octet order; valid count is in nibbles and remaining codes are returned separately as padding.

Why this case matters

Offline PCM interchange uses these exact bounded packet and sample representation decisions.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(octets, high_first, valid_nibbles):
    values=[]
    for byte in octets:
        high=byte>>4
        low=byte&15
        values.extend([high,low] if high_first else [low,high])
    count=min(max(valid_nibbles,0),len(values))
    return [values[:count],values[count:]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([24, 242], True, 3)), [[1, 8, 15], [2]])
check('oracle 2', solve(*([18, 52], False, 4)), [[2, 1, 4, 3], []])
check('oracle 3', solve(*([427], True, 2)), [[10, 11], []])
check('oracle 4', solve(*([], False, 0)), [[], []])
check('oracle 5', solve(*([128], False, 1)), [[0], [8]])
check('oracle 6', solve(*([255], True, 0)), [[], [15, 15]])
check('oracle 7', solve(*([87, 121], False, 8)), [[7, 5, 9, 7], []])
if N == 1: check('variant packet 1', solve(*[[24, 242, 24, 242], True, 6]), [[1, 8, 15, 2, 1, 8], [15, 2]])
if N == 2: check('variant packet 2', solve(*[[24, 242, 24, 242, 24, 242], True, 9]), [[1, 8, 15, 2, 1, 8, 15, 2, 1], [8, 15, 2]])
if N == 3: check('variant packet 3', solve(*[[24, 242, 24, 242, 24, 242, 24, 242], True, 12]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2], [1, 8, 15, 2]])
if N == 4: check('variant packet 4', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 15]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15], [2, 1, 8, 15, 2]])
if N == 5: check('variant packet 5', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 18]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8], [15, 2, 1, 8, 15, 2]])
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
oracle 1	`[[1, 8, 15], [2]]`	`[[1, 8, 15], [2]]`	Passed
oracle 2	`[[2, 1, 4, 3], []]`	`[[2, 1, 4, 3], []]`	Passed
oracle 3	`[[26, 11], []]`	`[[10, 11], []]`	Failed
oracle 4	`[[], []]`	`[[], []]`	Passed
oracle 5	`[[0], [8]]`	`[[0], [8]]`	Passed
oracle 6	`[[], [15, 15]]`	`[[], [15, 15]]`	Passed
oracle 7	`[[7, 5, 9, 7], []]`	`[[7, 5, 9, 7], []]`	Passed
variant packet 1	`[[1, 8, 15, 2, 1, 8], [15, 2]]`	`[[1, 8, 15, 2, 1, 8], [15, 2]]`	Passed

SHA-256 / 853bb1c3d573ecf066fec705bb2d6fd81ab8f982136a22ccd2c9eb29c6d737f4

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(octets, high_first, valid_nibbles):
    values=[]
    for byte in octets:
        high=byte&15
        low=byte&15
        values.extend([high,low] if high_first else [low,high])
    count=min(max(valid_nibbles,0),len(values))
    return [values[:count],values[count:]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([24, 242], True, 3)), [[1, 8, 15], [2]])
check('oracle 2', solve(*([18, 52], False, 4)), [[2, 1, 4, 3], []])
check('oracle 3', solve(*([427], True, 2)), [[10, 11], []])
check('oracle 4', solve(*([], False, 0)), [[], []])
check('oracle 5', solve(*([128], False, 1)), [[0], [8]])
check('oracle 6', solve(*([255], True, 0)), [[], [15, 15]])
check('oracle 7', solve(*([87, 121], False, 8)), [[7, 5, 9, 7], []])
if N == 1: check('variant packet 1', solve(*[[24, 242, 24, 242], True, 6]), [[1, 8, 15, 2, 1, 8], [15, 2]])
if N == 2: check('variant packet 2', solve(*[[24, 242, 24, 242, 24, 242], True, 9]), [[1, 8, 15, 2, 1, 8, 15, 2, 1], [8, 15, 2]])
if N == 3: check('variant packet 3', solve(*[[24, 242, 24, 242, 24, 242, 24, 242], True, 12]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2], [1, 8, 15, 2]])
if N == 4: check('variant packet 4', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 15]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15], [2, 1, 8, 15, 2]])
if N == 5: check('variant packet 5', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 18]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8], [15, 2, 1, 8, 15, 2]])
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
oracle 1	`[[8, 8, 2], [2]]`	`[[1, 8, 15], [2]]`	Failed
oracle 2	`[[2, 2, 4, 4], []]`	`[[2, 1, 4, 3], []]`	Failed
oracle 3	`[[11, 11], []]`	`[[10, 11], []]`	Failed
oracle 4	`[[], []]`	`[[], []]`	Passed
oracle 5	`[[0], [0]]`	`[[0], [8]]`	Failed
oracle 6	`[[], [15, 15]]`	`[[], [15, 15]]`	Passed
oracle 7	`[[7, 7, 9, 9], []]`	`[[7, 5, 9, 7], []]`	Failed
variant packet 1	`[[8, 8, 2, 2, 8, 8], [2, 2]]`	`[[1, 8, 15, 2, 1, 8], [15, 2]]`	Failed

SHA-256 / 3459eaae1962085f920471f7b82bdbf9cebcdec9b72c112f593775b056ae3eea

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(octets, high_first, valid_nibbles):
    values=[]
    for byte in octets:
        high=(byte>>4)&15
        low=byte&15
        values.extend([high,low] if high_first else [low,high])
    count=min(max(valid_nibbles,0),len(values))
    return [values[:count],values[count:]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('oracle 1', solve(*([24, 242], True, 3)), [[1, 8, 15], [2]])
check('oracle 2', solve(*([18, 52], False, 4)), [[2, 1, 4, 3], []])
check('oracle 3', solve(*([427], True, 2)), [[10, 11], []])
check('oracle 4', solve(*([], False, 0)), [[], []])
check('oracle 5', solve(*([128], False, 1)), [[0], [8]])
check('oracle 6', solve(*([255], True, 0)), [[], [15, 15]])
check('oracle 7', solve(*([87, 121], False, 8)), [[7, 5, 9, 7], []])
if N == 1: check('variant packet 1', solve(*[[24, 242, 24, 242], True, 6]), [[1, 8, 15, 2, 1, 8], [15, 2]])
if N == 2: check('variant packet 2', solve(*[[24, 242, 24, 242, 24, 242], True, 9]), [[1, 8, 15, 2, 1, 8, 15, 2, 1], [8, 15, 2]])
if N == 3: check('variant packet 3', solve(*[[24, 242, 24, 242, 24, 242, 24, 242], True, 12]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2], [1, 8, 15, 2]])
if N == 4: check('variant packet 4', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 15]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15], [2, 1, 8, 15, 2]])
if N == 5: check('variant packet 5', solve(*[[24, 242, 24, 242, 24, 242, 24, 242, 24, 242, 24, 242], True, 18]), [[1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8, 15, 2, 1, 8], [15, 2, 1, 8, 15, 2]])
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
oracle 1	`[[1, 8, 15], [2]]`	`[[1, 8, 15], [2]]`	Passed
oracle 2	`[[2, 1, 4, 3], []]`	`[[2, 1, 4, 3], []]`	Passed
oracle 3	`[[10, 11], []]`	`[[10, 11], []]`	Passed
oracle 4	`[[], []]`	`[[], []]`	Passed
oracle 5	`[[0], [8]]`	`[[0], [8]]`	Passed
oracle 6	`[[], [15, 15]]`	`[[], [15, 15]]`	Passed
oracle 7	`[[7, 5, 9, 7], []]`	`[[7, 5, 9, 7], []]`	Passed
variant packet 1	`[[1, 8, 15, 2, 1, 8], [15, 2]]`	`[[1, 8, 15, 2, 1, 8], [15, 2]]`	Passed

SHA-256 / 4f6a87c43584421013fac17a5e9bec4afd624413bad1362e9bea4f2fd23f9dba

Verification & scope

Stipulated finite model; no claim of hardware timing or full file-format conformance. 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 2026-09-29T14:45:03.057234+00:00.

Case digest / af8073e622ce50593abb4f9b3e72aa08e6681c8c3b6b3602b5926ef8b1739958