guava/src/com/google/common/primitives/ImmutableIntArray.java
public int indexOf(int target) {
    for (int i = start; i < end; i++) {
      if (array[i] == target) {
        return i - start;
      }
    }
    return -1;
  }
public int indexOf(int target) {
    for (int i = start; i < end; i++) {
      if (array[i] == target) {
        return i - start;
      }
    }
    return -1;
  }
Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no
such index exists. Equivalent to {@code asList().indexOf(target)}.