C/C++ base64 encoding/decoding

 

C++ base64 encoding

/*
  <Function Description>
    base64 encoding 함수.
 
  <parameter>
    in : 평문 문자열.
 
  <return>
    out : base64 encoding 문자열.
*/
std::string base64_encode(const std::string &in) {
 
    typedef unsigned char uchar;
    std::string out;   
 
    int val = 0, valb = -6;
    for (uchar c : in) {
        val = (val << 8) + c;
        valb += 8;
        while (valb >= 0) {
            out.push_back("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[(val >> valb) & 0x3F]);
            valb -= 6;
        }
    }
    if (valb > -6) out.push_back("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[((val << 8) >> (valb + 8)) & 0x3F]);
    while (out.size() % 4) out.push_back('=');
    return out;
}

 

C++ base64 decoding

/*
  <Function Description>
    base64 decode 함수.
 
  <parameter>
    in : base64 encoding 문자열.
 
  <return>
    out : base64 decoding 문자열.
*/
std::string base64_decode(const std::string &in) {
 
    typedef unsigned char uchar;
    static const std::string b = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
    std::string out;
    std::vector<int> T(256, -1);
 
    for (int i = 0; i < 64; i++)
        T[b[i]] = i;
 
    int val = 0, valb = -8;
 
    for (uchar c : in) {
        if (T[c] == -1)
            break;
 
        val = (val << 6) + T[c];
        valb += 6;
 
        if (valb >= 0) {
            out.push_back(char((val >> valb) & 0xFF));
            valb -= 8;
        }
    }
    return out;
}