int indexOfValue(Object value) {
        final int N = mSize * 2;
        final Object[] array = mArray;
        if (value == null) {
            for (int i = 1; i < N; i += 2) {
                if (array[i] == null) {
                    return i >> 1;
                }
            }
        } else {
            for (int i = 1; i < N; i += 2) {
                if (value.equals(array[i])) {
                    return i >> 1;
                }
            }
        }
        return -1;
    }
Returns the index of a key in the set.

@param key The key to search for.
@return Returns the index of the key if it exists, else a negative integer.
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/util/collection/SimpleArrayMap.java