有关下面C++代码的说法，错误的是（ ）。
double sqrt_binary(long long n, double epsilon = 1e-10) { if (n < 0) { throw invalid_argument("输入必须为非负整数"); } if (n == 0 || n == 1) return n; // 阶段 1 long long low = 1, high = n; long long k = 0; while (low <= high) { long long mid = (low + high) / 2; long long mid_sq = mid * mid; if (mid_sq == n) { return mid; } else if (mid_sq < n) { k = mid; low = mid + 1; } else { high = mid - 1; } } long long next_k = k + 1; if (next_k * next_k == n) { return next_k; } // 阶段 2 double low_d = (double)k; double high_d = (double)(k + 1); double mid; while (high_d - low_d >= epsilon) { mid = (low_d + high_d) / 2; double mid_sq = mid * mid; if (mid_sq < n) { low_d = mid; } else { high_d = mid; } } double result = (low_d + high_d) / 2; long long check_int = (long long)(result + 0.5); if (check_int * check_int == n) { return check_int; } return result;}