// int has 32 bits, which fits in each dimensions.
for (int j = 0; j < spec.getBitsPerDimension().size(); ++j) {
point[j].copyFrom(data[i][j]);
}
sfc.index(point, 0, index);
pairs.add(Pair.of(index.clone(), i));
}
// Sort by Hilbert index.
Collections.sort(pairs);
List<int[]> expected = new ArrayList<>(pairs.size());
for (Pair<BitVector, Integer> pair : pairs) {