FA-81691 / MIDI event timing / Open access

Loop-region playback event firing: playback may start on the loop end · case 01

Starting playback exactly at the loop end is accepted and immediately wraps, instead of being rejected.

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

ROOT CAUSE

The start guard permits a start position equal to the loop end.

THE FAILURE

The start guard permits a start position equal to the loop end.

Unsuccessful approach: Allowing one more tick is the same off-by-one.

Case contract

Input [loop_start, loop_end, events, from_tick, to_tick]. Playback runs over playback ticks p in [from, to). Song position is p while p < loop_end, afterwards loop_start + (p - loop_end) mod (loop_end - loop_start). Every event whose song tick equals the song position fires as [p, event_tick]. Requires 0 <= loop_start < loop_end and 0 <= from < loop_end, else None.

Why this case matters

MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 5:
        return None
    ls, le, events, start, stop = x
    if not 0 <= ls < le or start > le or start < 0:
        return None
    L = le - ls
    hits = []
    for p in range(start, stop):
        song = p if p < le else ls + (p - le) % L
        for e in sorted(events):
            if e == song:
                hits.append([p, e])
    return hits
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None)], [([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None), ([4, 8, [4], 9, 10], None), ([4, 8, [4], 3, 12], [[4, 4], [8, 4]]), ([5, 5, [5], 0, 5], None)], [([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None), ([4, 8, [4], 9, 10], None), ([4, 8, [4], 3, 12], [[4, 4], [8, 4]]), ([5, 5, [5], 0, 5], None), ([4, 8, [4], -1, 4], None), ([10, 20, [12, 19], 15, 40], [[19, 19], [22, 12], [29, 19], [32, 12], [39, 19]]), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])], [([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([4, 8, [4], 8, 9], None), ([5, 5, [5], 0, 5], None), ([4, 8, [4], -1, 4], None), ([10, 20, [12, 19], 15, 40], [[19, 19], [22, 12], [29, 19], [32, 12], [39, 19]]), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])], [([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([4, 8, [4], 8, 9], None), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
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 0	`[[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]`	`[[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]`	Passed
oracle 1	`[]`	`[]`	Passed
oracle 2	`[[7, 7], [11, 7], [15, 7], [19, 7]]`	`[[7, 7], [11, 7], [15, 7], [19, 7]]`	Passed
oracle 3	`[[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]`	`[[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]`	Passed
oracle 4	`[[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]`	`[[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]`	Passed
oracle 5	`[[9, 5], [13, 5]]`	`[[9, 5], [13, 5]]`	Passed
oracle 6	`[[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]`	`[[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]`	Passed
oracle 7	`[[8, 4]]`	`None`	Failed

SHA-256 / 2009fe220e1abcbdeb1e7dd603052ff3a7565590d0e65c0e38cba4ebaa55affb

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    if not isinstance(x, list) or len(x) != 5:
        return None
    ls, le, events, start, stop = x
    if not 0 <= ls < le or start >= le + 1 or start < 0:
        return None
    L = le - ls
    hits = []
    for p in range(start, stop):
        song = p if p < le else ls + (p - le) % L
        for e in sorted(events):
            if e == song:
                hits.append([p, e])
    return hits
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None)], [([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None), ([4, 8, [4], 9, 10], None), ([4, 8, [4], 3, 12], [[4, 4], [8, 4]]), ([5, 5, [5], 0, 5], None)], [([3, 5, [3, 4, 5], 0, 12], [[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]), ([4, 8, [4], 8, 9], None), ([4, 8, [4], 9, 10], None), ([4, 8, [4], 3, 12], [[4, 4], [8, 4]]), ([5, 5, [5], 0, 5], None), ([4, 8, [4], -1, 4], None), ([10, 20, [12, 19], 15, 40], [[19, 19], [22, 12], [29, 19], [32, 12], [39, 19]]), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])], [([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([4, 8, [4], 8, 9], None), ([5, 5, [5], 0, 5], None), ([4, 8, [4], -1, 4], None), ([10, 20, [12, 19], 15, 40], [[19, 19], [22, 12], [29, 19], [32, 12], [39, 19]]), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])], [([4, 8, [4, 6], 0, 16], [[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]), ([4, 8, [8], 0, 16], []), ([4, 8, [7], 0, 20], [[7, 7], [11, 7], [15, 7], [19, 7]]), ([2, 6, [0, 2, 5], 0, 14], [[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]), ([0, 4, [0, 3], 0, 10], [[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]), ([4, 8, [1, 5], 6, 14], [[9, 5], [13, 5]]), ([4, 8, [4], 8, 9], None), ([1, 9, [1, 8], 0, 20], [[1, 1], [8, 8], [9, 1], [16, 8], [17, 1]])]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("oracle %d" % i, solve(args), expected)
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 0	`[[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]`	`[[4, 4], [6, 6], [8, 4], [10, 6], [12, 4], [14, 6]]`	Passed
oracle 1	`[]`	`[]`	Passed
oracle 2	`[[7, 7], [11, 7], [15, 7], [19, 7]]`	`[[7, 7], [11, 7], [15, 7], [19, 7]]`	Passed
oracle 3	`[[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]`	`[[0, 0], [2, 2], [5, 5], [6, 2], [9, 5], [10, 2], [13, 5]]`	Passed
oracle 4	`[[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]`	`[[0, 0], [3, 3], [4, 0], [7, 3], [8, 0]]`	Passed
oracle 5	`[[9, 5], [13, 5]]`	`[[9, 5], [13, 5]]`	Passed
oracle 6	`[[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]`	`[[3, 3], [4, 4], [5, 3], [6, 4], [7, 3], [8, 4], [9, 3], [10, 4], [11, 3]]`	Passed
oracle 7	`[[8, 4]]`	`None`	Failed

SHA-256 / 78017c96e9a4a6a6d61fdf3209ebd4bf0f20f5baeea7f68b14d7494f4d87b895

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic bounded teaching model with a stipulated toy contract; it is not a complete Standard MIDI File or MIDI 1.0/2.0 implementation. 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 2026-09-29T14:50:05.249252+00:00.

Case digest / 51ed022aeca4bd65545ae4927e1326443a717ca32bf1bee33a76c563f77906d0