Basic Base64 encoding

base64.cpp

// Reference: https://en.wikipedia.org/wiki/Base64
#include <bits/stdc++.h>
using namespace std;

const char* alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int getValue(char c) {
    int len = strlen(alphabet);
    for (int i = 0; i < len; i++) {
        if (c == alphabet[i]) { return i; }
    }
    return -1;
}

string encode(string str) {
    string bits;
    for (char c : str) {
        int x = c;
        for (int i = 7; i >= 0; i--) {
            if (x & (1<<i)) {
                bits += '1';
            } else {
                bits += '0';
            }
        }
    }
    while (bits.size() % 6 != 0) {
        bits += '0';
    }


    string encoded;
    for (int i = 0; i < bits.size(); i += 6) {
        int v = 0;
        for (int j = 0; j < 6; j++) {
            v = v * 2 + (bits[i+j] - '0');
        }
        encoded += alphabet[v];
    }
    while (encoded.size() % 4 != 0) {
        encoded += "=";
    }

    return encoded;
}

string tobin(int v) {
    string bits;
    while (v > 0) {
        bits += char(v % 2 + '0');
        v /= 2;
    }
    while (bits.size() < 6) {
        bits += '0';
    }
    reverse(begin(bits), end(bits));
    return bits;
}

string decode(string str) {
    string bits;
    for (int i = 0; i < str.size(); i++) {
        if (str[i] == '=') { break; }
        int v = getValue(str[i]);
        bits += tobin(v);
    }

    string decoded;
    for (int i = 0; i < bits.size(); i += 8) {
        int c = 0;
        for (int j = 0; j < 8 && i + j < bits.size(); j++) {
            c = c * 2 + (bits[i+j] - '0');
        }
        if (c > 0) {
            decoded += char(c);
        }
    }
    return decoded;
}

int main() {
    vector<string> examples{
        "Many hands make light work.",
        "Man",
        "Ma",
        "M",
        "light work.",
        "light work",
        "light wor",
        "light wo",
        "light w"
    };
    for (auto& example : examples) {
        string enc = encode(example);
        cout << "Example: " << example << "\n";
        cout << "Encoded: " << enc << "\n";
        cout << "Decoded: " << decode(enc) << "\n\n";
    }

    return 0;
}