FAILURE MAP
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FA-11621 / Compression format semantics / Open access

Delta decompression carries a predictor across independent blocks · case 01

Delta decompression carries a predictor across independent blocks.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The previous block last value seeds the next independent block.

VERIFIED REPAIR

Initialize the predictor at the beginning of every independent block and accumulate all deltas within that block.

Unsuccessful approach: Treating each delta as absolute avoids carryover but loses within-block accumulation.

Case contract

Each list is an independent delta-coded block whose predictor starts at zero. Return corresponding lists of prefix sums; empty blocks remain empty.

Why this case matters

A small offline codec model isolates a compression-specific failure without external files or libraries.

1 / The failure

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

N = 1
observations = []
def solve(blocks):
    out=[]; previous=0
    for block in blocks:
        row=[]
        for d in block: previous+=d; row.append(previous)
        out.append(row)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('reset boundary',solve([[N,1],[2,1]]),[[N,N+1],[2,3]])
check('empty',solve([]),[])
check('empty block',solve([[],[1]]),[[],[1]])
check('negative delta',solve([[3,-2]]),[[3,1]])
check('zero delta',solve([[2,0,0]]),[[2,2,2]])
check('singletons',solve([[2],[3]]),[[2],[3]])
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
reset boundary[[1, 2], [4, 5]][[1, 2], [2, 3]]Failed
empty[][]Passed
empty block[[], [1]][[], [1]]Passed
negative delta[[3, 1]][[3, 1]]Passed
zero delta[[2, 2, 2]][[2, 2, 2]]Passed
singletons[[2], [5]][[2], [3]]Failed

SHA-256 / a099b071455873a11594683fdd6ce3598f51df22d35dd2605b070037c0bc65e2

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(blocks):
    return blocks
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('reset boundary',solve([[N,1],[2,1]]),[[N,N+1],[2,3]])
check('empty',solve([]),[])
check('empty block',solve([[],[1]]),[[],[1]])
check('negative delta',solve([[3,-2]]),[[3,1]])
check('zero delta',solve([[2,0,0]]),[[2,2,2]])
check('singletons',solve([[2],[3]]),[[2],[3]])
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
reset boundary[[1, 1], [2, 1]][[1, 2], [2, 3]]Failed
empty[][]Passed
empty block[[], [1]][[], [1]]Passed
negative delta[[3, -2]][[3, 1]]Failed
zero delta[[2, 0, 0]][[2, 2, 2]]Failed
singletons[[2], [3]][[2], [3]]Passed

SHA-256 / 308f0cf7d67bcef68f9e0693018243fad96a6450cc27f03423b5183bcf7c3cf7

3 / The verified repair

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

N = 1
observations = []
def solve(blocks):
    out=[]
    for block in blocks:
        previous=0; row=[]
        for d in block: previous+=d; row.append(previous)
        out.append(row)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('reset boundary',solve([[N,1],[2,1]]),[[N,N+1],[2,3]])
check('empty',solve([]),[])
check('empty block',solve([[],[1]]),[[],[1]])
check('negative delta',solve([[3,-2]]),[[3,1]])
check('zero delta',solve([[2,0,0]]),[[2,2,2]])
check('singletons',solve([[2],[3]]),[[2],[3]])
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
reset boundary[[1, 2], [2, 3]][[1, 2], [2, 3]]Passed
empty[][]Passed
empty block[[], [1]][[], [1]]Passed
negative delta[[3, 1]][[3, 1]]Passed
zero delta[[2, 2, 2]][[2, 2, 2]]Passed
singletons[[2], [3]][[2], [3]]Passed

SHA-256 / 3cd6a2a7d2d80d812e2474b2c3946d64d594d7ac79f64581fd0ec33705228d63

Verification & scope

Controlled educational model, not a complete implementation of a production compression format. 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 2026-09-29T14:38:49.542241+00:00.

Case digest / 4ab5b990ea4ae7e9bc20da011716e31a8ae567cc7b79925f9378ad7f6af75cd6