code: public int indexOfValue(int value) {
          for (int i = 0; i < mSize; i++)
              if (mValues[i] == value)
                  return i;
  
          return -1;
      }
docs: Returns an index for which {@link #valueAt} would return the
  specified key, or a negative number if no keys map to the
  specified value.
  Beware that this is a linear search, unlike lookups by key,
  and that multiple keys can map to the same value and this will
  find only one of them.