_singleTransform4(data, out, outOff, off, step, inv) {
        // radix-4
        // NOTE: Only called for len=8
        const step2 = step * 2;
        const step3 = step * 3;

        // Original values
        const Ar = data[off];
        const Ai = data[off + 1];
        const Br = data[off + step];
        const Bi = data[off + step + 1];
        const Cr = data[off + step2];
        const Ci = data[off + step2 + 1];
        const Dr = data[off + step3];
        const Di = data[off + step3 + 1];

        // Pre-Final values
        const T0r = Ar + Cr;
        const T0i = Ai + Ci;
        const T1r = Ar - Cr;
        const T1i = Ai - Ci;
        const T2r = Br + Dr;
        const T2i = Bi + Di;
        const T3r = inv * (Br - Dr);
        const T3i = inv * (Bi - Di);

        // Final values
        out[outOff] = T0r + T2r;
        out[outOff + 1] = T0i + T2i;
        out[outOff + 2] = T1r + T3i;
        out[outOff + 3] = T1i - T3r;
        out[outOff + 4] = T0r - T2r;
        out[outOff + 5] = T0i - T2i;
        out[outOff + 6] = T1r - T3i;
        out[outOff + 7] = T1i + T3r;
    }
Performs radix-4 transformation on input data of length 8

@param {Float64Array} data Input data array of length 8
@param {Float64Array} out Output data array of length 8
@param {number} outOff Index of output array to start writing from
@param {number} off Index of input array to start reading from
@param {number} step Step size between elements in input array
@param {number} inv Scaling factor for inverse transform

@returns {void}