public static int hashCode(int i1, int i2, int i3, int i4) {
    int acc = X + i1;
    acc = X * acc + i2;
    acc = X * acc + i3;
    acc = X * acc + i4;
    return acc;
  }
Hash code is computed as value of polynomial whose coefficients are determined by hash codes of
objects passed as parameter to one of hashCode functions. More precisely: hashCode(o1, o2, ...,
on) = P[o1, o2, ..., on](X) = X^n + o1.hashCode() * X ^ (n - 1) + o2.hashCode() * X ^ (n - 2) +
... + on.hashCode() * X ^ 0

<p>Constant X determines point at which polynomial is evaluated.
fbcore/src/main/java/com/facebook/common/util/HashCodeUtil.java