FA-10701 / Rendering state / Open access
Stencil increment saturates · case 01
Stencil increment wraps a saturated 255 value back to zero.
ROOT CAUSE
Stencil increment wraps a saturated 255 value back to zero.
VERIFIED REPAIR
Use the stage contract: Increment a stencil byte using the saturating increment operation, distinct from increment-and-wrap.
Unsuccessful approach: A ceiling of 254 excludes the valid maximal stencil value.
Case contract
Increment a stencil byte using the saturating increment operation, distinct from increment-and-wrap.
Why this case matters
A deterministic software graphics stage with explicit channel and coordinate conventions; no hardware, device profile or API behavior is inferred.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(value):
return (value+1)&255
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(255,)), 255)
check('fixture 2', solve(*(254,)), 255)
check('fixture 3', solve(*(0,)), 1)
check('fixture 4', solve(*(100,)), 101)
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 | 0 | 255 | Failed |
| fixture 2 | 255 | 255 | Passed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 101 | 101 | Passed |
SHA-256 / 1e9b3351dbf59c3ab9ce5e078284664dcf73c2ca4f614eb8bef2e8ff52d93778
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(value):
return min(254,value+1)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(255,)), 255)
check('fixture 2', solve(*(254,)), 255)
check('fixture 3', solve(*(0,)), 1)
check('fixture 4', solve(*(100,)), 101)
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 | 254 | 255 | Failed |
| fixture 2 | 254 | 255 | Failed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 101 | 101 | Passed |
SHA-256 / 6fa26c07c855310b356c0bb25a63633561654d29e02f44a8afcdf7525bc96a52
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(value):
return min(255,value+1)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(255,)), 255)
check('fixture 2', solve(*(254,)), 255)
check('fixture 3', solve(*(0,)), 1)
check('fixture 4', solve(*(100,)), 101)
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 | 255 | 255 | Passed |
| fixture 2 | 255 | 255 | Passed |
| fixture 3 | 1 | 1 | Passed |
| fixture 4 | 101 | 101 | Passed |
SHA-256 / d94141c64a494572cadd34d35ef490b41e891fe8f90b2cf1007c2a6e8848cb49
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 2026-09-29T14:38:41.357607+00:00.
Case digest / dfb68e86ae478826b9c9064ff896b474faa7908425e8f1fc9c5b4799169d0697