private static int indexOf(final int[] a, final int start, final int value) {
		for (int i = start; i >= 0; --i) {
			if (a[i] < value) {
				return -1;
			} else if (a[i] == value) {
				return i;
			}
		}

		return -1;
	}
Selects a random subset of size {@code k} from a set of size {@code n}.

@param n the size of the set.
@param k the size of the subset.
@param rnd the random number generator used.
@throws NullPointerException if {@code random} is {@code null}.
@throws IllegalArgumentException if {@code n < k}, {@code k == 0} or if
        {@code n*k} will cause an integer overflow.
@return the a-set array for the given parameter. The returned subset
        array is sorted in increasing order.
jenetics/src/main/java/io/jenetics/internal/math/Subsets.java