达夫设备(duff`s device)减少迭代次数

var iterations = Math.floor(items.length / 8),
    startAt = items.length % 8,
    i = 0;

do {
    switch (startAt) {
        case 0:
            process(items[i++]);
        case 7:
            process(items[i++]);
        case 6:
            process(items[i++]);
        case 5:
            process(items[i++]);
        case 4:
            process(items[i++]);
        case 3:
            process(items[i++]);
        case 2:
            process(items[i++]);
        case 1:
            process(items[i++]);
    }
    startAt = 0;
} while (--iterations)