code: private int checkAndGetTotalCount() throws IllegalStateException {
  		int usedBuckets = 0;
  		int totalCount = buckets[0].getCount();
  		for (int i = 1; i <= bucketNb; i++) {
  			int bucketCount = buckets[i].getCount();
  			totalCount += bucketCount;
  			if (bucketCount > 0) {
  				usedBuckets++;
  			}
  		}
  		totalCount += buckets[bucketNb + 1].getCount();
  		if (usedBuckets < 3) {
  			throw new IllegalStateException("Only " + usedBuckets + " buckets used, not enough for interpolation, consider reconfiguring min/max/nb");
  		}
  		return totalCount;
  	}
docs: Computes expected count and check used buckets number.