/**
* Constructor.
*
* @param pr pre values
* @param ps positions
*/
private FTCache(final IntList pr, final IntList ps) {
final int s = pr.size();
final double[] v = new double[s];
for (int i = 0; i < s; i++) v[i] = (long) pr.get(i) << 32 | ps.get(i);
order = Array.createOrder(v, true);
pre = pr;
pos = ps;
}
