Returns intervals of CZPowGate exponents valid for FSim decomposition.

Ideal intervals associated with the constraints are closed, but due to numerical error the caller should not assume the endpoints themselves are valid for the decomposition. See decompose_cphase_into_two_fsim for details on how FSimGate parameters constrain the phase angle of CZPowGate.

fsim_gate FSimGate into which CZPowGate would be decomposed.

Sequence of 2-tuples each consisting of the minimum and maximum value of the exponent for which CZPowGate can be decomposed into two FSimGates. The intervals are cropped to [0, 2]. The function returns zero, one or two intervals.