FA-91303 / Quantum circuit simulation / Member archive

Register expansion accepts index equal to register size · case 03

h q[2] on a two-qubit register maps to the first qubit of the next register (or a phantom qubit).

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input a list of OpenQASM-2-like statements: "qreg n[k];", "creg n[k];", gate statements "g a,b;" and "measure a -> b;" where operands are whole registers or "n[i]". Registers are flattened in declaration order per kind (qubits and clbits have separate counters). Whole-register operands broadcast; a single qubit operand is reused across the broadcast. Return [[g, [flat qubits]] or ["measure", q, c]...] or [error, statement index] with errors "unknown-register", "index-out-of-range", "size-mismatch".

Why this case matters

Front-end register flattening decides which physical qubits every later pass touches; offset or broadcast slips silently rewire circuits.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: random program 46	`[["measure", 2, 1], ["cx", [3, 6]], ["cx", [4, 6]], ["cx", [5, 6]]]`	`["index-out-of-range", 7]`	Failed

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