优化基准之间的转换-C ++

Question

I am designing a cipher and need to convert between bases repeatedly in a loop. I have optimized the everything else, but I'm not too familiar with C++ code, and and am trying to figure out how to make the conversion faster.

Here's the current code I'm using:

string digits = "0123456789abcdef";
string tohex(string number) {                        // Decimal to Hexadecimal function
    long length = number.length();
    string result = "";
    vector<long> nibbles;
    for ( long i = 0; i < length; i++ ) {
        nibbles.push_back(digits.find(number[i]));
    }
    long newlen = 0;
    do {
        long value = 0;
        newlen = 0;
        for ( long i = 0; i < length; i++ ) {
            value = (value * 10) + nibbles[i];
            if (value >= 16) {
                nibbles[newlen++] = value / 16;
                value %= 16;
            } else if (newlen > 0) {
                nibbles[newlen++] = 0;
            };
        };
        length = newlen;
        result = digits[value] + result;
    } while (newlen != 0);
    return result;
}

Answer 1

In my case (cipher) the number will always fit within an int, so it works to do:

string tohex(string number) {
    int num = std::stoi(number);
    std::stringstream hexnumber;
    hexnumber << std::hex << num;
    return hexnumber.str();
}

This is better because it is simpler and uses the built-in std::hex method.