Unique Hash

#include <iostream>
#include <string>
#include <stdexcept>

constexpr uint64_t operator "" _uniq_hash(char const * str, size_t len) {
    return len > sizeof(uint64_t) / sizeof(char)
        ? throw std::length_error("str")
        : len == 0
            ? 0
            : *str + (operator "" _uniq_hash(str + 1, len - 1) << sizeof(char) * 8);
}

uint64_t get_uniq_hash(const std::string& str) {
    if (str.length() > sizeof(uint64_t) / sizeof(char))
        throw std::length_error("str");

    uint64_t result = 0;
    for (auto rit = str.rbegin(); rit != str.rend(); ++rit) {
        result <<= sizeof(char) * 8;
        result += *rit;
    }
    return result;
}

int main() {
    using namespace std;
    string word;
    while (cin >> word) {
        if (word.length() < sizeof(uint64_t)) {
            switch (get_uniq_hash(word)) {
            case "zero"_uniq_hash:
            case "one"_uniq_hash:
            case "two"_uniq_hash:
            case "three"_uniq_hash:
            case "four"_uniq_hash:
            case "five"_uniq_hash:
            case "six"_uniq_hash:
            case "seven"_uniq_hash:
            case "eight"_uniq_hash:
            case "nine"_uniq_hash:
                cout << "A number" << endl;
                continue;
            }
        }
        cout << "Not a number" << endl;
    }
}