uECC_VLI_API uECC_word_t uECC_vli_add(uECC_word_t *result,
                                      const uECC_word_t *left,
                                      const uECC_word_t *right,
                                      wordcount_t num_words) {
    uECC_word_t carry = 0;
    wordcount_t i;
    for (i = 0; i < num_words; ++i) {
        uECC_word_t sum = left[i] + right[i] + carry;
        if (sum != left[i]) {
            carry = (sum < left[i]);
        }
        result[i] = sum;
    }
    return carry;
}