FA-10786 / PCM sample encoding / Open access

Signed sixteen little endian decode · case 01

Byte order swaps the significance of each PCM sample byte.

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

ROOT CAUSE

Byte order swaps the significance of each PCM sample byte.

VERIFIED REPAIR

Apply the explicit PCM/playback contract: Decode a byte-value list of even length as signed 16-bit little-endian PCM samples.

Unsuccessful approach: Correcting endianness while retaining unsigned interpretation makes negative samples positive.

Case contract

Decode a byte-value list of even length as signed 16-bit little-endian PCM samples.

Why this case matters

A pure Python local audio pipeline stage with explicit sample formats and frame conventions; no real-time device or signal-spectrum claims.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(data):
    return [int.from_bytes(bytes(data[i:i+2]),"big",signed=True) for i in range(0,len(data),2)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([0, 128, 255, 127],)),[-32768, 32767])
check('fixture 2',solve(*([1, 0, 255, 255],)),[1, -1])
check('fixture 3',solve(*([],)),[])
check('fixture 4',solve(*([0, 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
fixture 1	`[128, -129]`	`[-32768, 32767]`	Failed
fixture 2	`[256, -1]`	`[1, -1]`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[0]`	`[0]`	Passed

SHA-256 / 2c408f56b3210792e500d13ad15f053d221dba75fbe09f268d1fc4fde74e5d69

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(data):
    return [int.from_bytes(bytes(data[i:i+2]),"little",signed=False) for i in range(0,len(data),2)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([0, 128, 255, 127],)),[-32768, 32767])
check('fixture 2',solve(*([1, 0, 255, 255],)),[1, -1])
check('fixture 3',solve(*([],)),[])
check('fixture 4',solve(*([0, 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
fixture 1	`[32768, 32767]`	`[-32768, 32767]`	Failed
fixture 2	`[1, 65535]`	`[1, -1]`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[0]`	`[0]`	Passed

SHA-256 / ee9c6af23b414cb72ed3ab04494c652a933730d23b8e3d3a20d676667ef4063e

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(data):
    return [int.from_bytes(bytes(data[i:i+2]),"little",signed=True) for i in range(0,len(data),2)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*([0, 128, 255, 127],)),[-32768, 32767])
check('fixture 2',solve(*([1, 0, 255, 255],)),[1, -1])
check('fixture 3',solve(*([],)),[])
check('fixture 4',solve(*([0, 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
fixture 1	`[-32768, 32767]`	`[-32768, 32767]`	Passed
fixture 2	`[1, -1]`	`[1, -1]`	Passed
fixture 3	`[]`	`[]`	Passed
fixture 4	`[0]`	`[0]`	Passed

SHA-256 / 83eb6a9f56d0fe3d08b73e06e594d3839ee93665de4ab9f1a84c139d2a026e49

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 2026-09-29T14:38:42.227296+00:00.

Case digest / 45475bacb7284ac1d5130dccd9d1f251908ab195dea74f9c92d13f805d488e3d