FA-89276 / Digital logic simulation / Open access

Scan-out observed after the shift edge · case 01

The unloaded bit stream is missing the first bit and one position late.

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ROOT CAUSE

Scan-out is read after the shift updated the chain.

THE FAILURE

Scan-out is read after the shift updated the chain.

Unsuccessful approach: Observing the first flop reads the wrong end of the chain.

Case contract

Input [chain, logic, state, ops]: chain lists flops from scan-in to scan-out. 'shift' with bit b: scan-out observes the last flop before the edge, then every flop takes its predecessor's old value and the first takes b. 'capture': every flop loads its functional next state logic[f] = [op, inputs] (and/xor/not) computed from the old state of all flops simultaneously. Return [scan-out bits, final chain values].

Why this case matters

Scan-based test simulation must shift and capture as simultaneous register updates.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(*args):
    chain, logic, state, ops = args
    state = dict(state)
    sout = []
    for op, bit in ops:
        if op == 'shift':
            vals = [bit] + [state[f] for f in chain[:-1]]
            for f, v in zip(chain, vals):
                state[f] = v
            sout.append(state[chain[-1]])
        else:
            nxt = {}
            for f in chain:
                kind, ins = logic[f]
                bits = [state[i] for i in ins]
                nxt[f] = int(all(bits)) if kind == 'and' else (sum(bits) % 2 if kind == 'xor' else 1 - bits[0])
            state.update(nxt)
    return [sout, [state[f] for f in chain]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1], ['shift', 0]]], [[1, 1], [0, 1, 1, 0]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1]]], [[0], [1, 1, 0, 0]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1]]], [[1, 0], [1, 1, 0, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['shift', 1], ['shift', 0], ['shift', 1]]], [[0, 1, 0], [1, 0, 1, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[1, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1]]], [[1, 0], [1, 1, 1, 0]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1], [1, 1, 1, 0]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1]]], [[1], [1, 1, 0, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1]]], [[0, 0, 0], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0], [1, 1, 1, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['shift', 1], ['shift', 0]]], [[0, 1], [0, 1, 1, 0]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[1, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 0, 1], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0, 1], [1, 1, 1, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1], ['shift', 0], ['shift', 1]]], [[1, 1, 0], [1, 0, 1, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[0, 0, 0, 1, 1], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0, 1, 1], [1, 1, 1, 1]])]]
for label, args, expected in fixtures[N-1]:
    check(label, 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
shift in a pattern	`[[1, 0], [0, 1, 1, 0]]`	`[[1, 1], [0, 1, 1, 0]]`	Failed
capture then unload	`[[0, 1, 1, 0], [0, 0, 0, 0]]`	`[[0, 0, 1, 1], [0, 0, 0, 0]]`	Failed
load capture unload	`[[0, 0, 0, 0], [0, 0, 1, 0]]`	`[[0, 0, 0, 0], [0, 0, 1, 0]]`	Passed
double capture	`[[0], [1, 1, 0, 0]]`	`[[0], [1, 1, 0, 0]]`	Passed
short chain	`[[1, 0], [1, 0]]`	`[[0, 1], [1, 0]]`	Failed
flush ones	`[[0, 1], [1, 1, 0, 1]]`	`[[1, 0], [1, 1, 0, 1]]`	Failed

SHA-256 / 39868458646b5b5ce8310eb765c422dff8ee3d1ccd4c7ccd64240dc9777cf70b

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(*args):
    chain, logic, state, ops = args
    state = dict(state)
    sout = []
    for op, bit in ops:
        if op == 'shift':
            sout.append(state[chain[0]])
            vals = [bit] + [state[f] for f in chain[:-1]]
            for f, v in zip(chain, vals):
                state[f] = v
        else:
            nxt = {}
            for f in chain:
                kind, ins = logic[f]
                bits = [state[i] for i in ins]
                nxt[f] = int(all(bits)) if kind == 'and' else (sum(bits) % 2 if kind == 'xor' else 1 - bits[0])
            state.update(nxt)
    return [sout, [state[f] for f in chain]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1], ['shift', 0]]], [[1, 1], [0, 1, 1, 0]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1]]], [[0], [1, 1, 0, 0]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1]]], [[1, 0], [1, 1, 0, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['shift', 1], ['shift', 0], ['shift', 1]]], [[0, 1, 0], [1, 0, 1, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[1, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1]]], [[1, 0], [1, 1, 1, 0]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1], [1, 1, 1, 0]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1]]], [[1], [1, 1, 0, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1]]], [[0, 0, 0], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0], [1, 1, 1, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['shift', 1], ['shift', 0]]], [[0, 1], [0, 1, 1, 0]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[1, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 0}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 0, 1], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0, 1], [1, 1, 1, 1]])], [('shift in a pattern', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['shift', 1], ['shift', 0], ['shift', 1]]], [[1, 1, 0], [1, 0, 1, 1]]), ('capture then unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['shift', 0], ['shift', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 1, 1], [0, 0, 0, 0]]), ('load capture unload', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 0, 'f2': 0, 'f3': 0}, [['shift', 1], ['shift', 1], ['capture', 0], ['shift', 0], ['shift', 0]]], [[0, 0, 0, 0], [0, 0, 1, 0]]), ('double capture', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 1, 'f1': 0, 'f2': 1, 'f3': 1}, [['capture', 0], ['capture', 0], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[0, 0, 0, 1, 1], [1, 1, 1, 1]]), ('short chain', [['f0', 'f2'], {'f0': ['not', ['f2']], 'f2': ['xor', ['f0', 'f2']]}, {'f0': 1, 'f2': 0}, [['shift', 0], ['capture', 0], ['shift', 1]]], [[0, 1], [1, 0]]), ('flush ones', [['f0', 'f1', 'f2', 'f3'], {'f0': ['xor', ['f1', 'f2']], 'f1': ['and', ['f0', 'f2']], 'f2': ['not', ['f0']], 'f3': ['xor', ['f2', 'f3']]}, {'f0': 0, 'f1': 1, 'f2': 0, 'f3': 1}, [['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1], ['shift', 1]]], [[1, 0, 1, 0, 1, 1], [1, 1, 1, 1]])]]
for label, args, expected in fixtures[N-1]:
    check(label, 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
shift in a pattern	`[[1, 1], [0, 1, 1, 0]]`	`[[1, 1], [0, 1, 1, 0]]`	Passed
capture then unload	`[[1, 0, 0, 0], [0, 0, 0, 0]]`	`[[0, 0, 1, 1], [0, 0, 0, 0]]`	Failed
load capture unload	`[[0, 1, 1, 0], [0, 0, 1, 0]]`	`[[0, 0, 0, 0], [0, 0, 1, 0]]`	Failed
double capture	`[[1], [1, 1, 0, 0]]`	`[[0], [1, 1, 0, 0]]`	Failed
short chain	`[[1, 0], [1, 0]]`	`[[0, 1], [1, 0]]`	Failed
flush ones	`[[0, 1], [1, 1, 0, 1]]`	`[[1, 0], [1, 1, 0, 1]]`	Failed

SHA-256 / ff5f94a6f79e84f1df97ede1d6b6201e3ef0bf2f51be255aeead98318a5d0035

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 6 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.

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Verification & scope

A deterministic bounded teaching model of one simulator rule set; the contract is stipulated and is not a claim of conformance to any HDL standard or commercial simulator. 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 2026-09-29T14:51:16.015525+00:00.

Case digest / 68ca8e5d24fb4601e4ceccc92fd83d5ea5c159927c32841ff3566a6fab9b6ba4