Base64.cpp

#include <samchon/library/Base64.hpp>

#include <array>

using namespace std;
using namespace samchon;
using namespace samchon::library;

/* -------------------------------------------------------------------------
    ENCODE
------------------------------------------------------------------------- */
auto Base64::encode(const ByteArray &byteArray) -> string
{
    static array<char, 64> base64CharArray =
    {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
        'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
        'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
        'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
        'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
        'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
        'w', 'x', 'y', 'z', '0', '1', '2', '3',
        '4', '5', '6', '7', '8', '9', '+', '/'
    };

    unsigned char *bytes = (unsigned char*)byteArray.data();
    string str;
    str.reserve(byteArray.size() * 4);
    
    long long leftSize = (long long)byteArray.size();

    size_t i = 0;
    size_t j = 0;
    array<unsigned char, 3> input;
    array<unsigned char, 4> output;

    while (leftSize--)
    {
        input[i++] = *(bytes++);
        if (i == 3)
        {
            output[0] = (input[0] & 0xfc) >> 2;
            output[1] = ((input[0] & 0x03) << 4) + ((input[1] & 0xf0) >> 4);
            output[2] = ((input[1] & 0x0f) << 2) + ((input[2] & 0xc0) >> 6);
            output[3] = input[2] & 0x3f;

            for (i = 0; (i < 4); i++)
                str += base64CharArray[output[i]];
            i = 0;
        }
    }

    if (i)
    {
        for (j = i; j < 3; j++)
            input[j] = '\0';

        output[0] = (input[0] & 0xfc) >> 2;
        output[1] = ((input[0] & 0x03) << 4) + ((input[1] & 0xf0) >> 4);
        output[2] = ((input[1] & 0x0f) << 2) + ((input[2] & 0xc0) >> 6);
        output[3] = input[2] & 0x3f;

        for (j = 0; (j < i + 1); j++)
            str += base64CharArray[output[j]];

        while ((i++ < 3))
            str += '=';

    }
    return str;
}

/* -------------------------------------------------------------------------
    DECODE
------------------------------------------------------------------------- */
auto Base64::decode(const std::string &str) -> ByteArray
{
    static array<int, 256> base64DecodeArray =
    {
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 00-0F */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 10-1F */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,  /* 20-2F */
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,  /* 30-3F */
        -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,  /* 40-4F */
        15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,  /* 50-5F */
        -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,  /* 60-6F */
        41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,  /* 70-7F */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 80-8F */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 90-9F */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* A0-AF */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* B0-BF */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* C0-CF */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* D0-DF */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* E0-EF */
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1   /* F0-FF */
    };

    ByteArray data;
    data.reserve(str.size() * 3);

    int space_idx = 0, phase;
    int d, prev_d = 0;
    unsigned char c;

    space_idx = 0;
    phase = 0;

    for (size_t i = 0; i < str.size(); i++)
{
        d = base64DecodeArray[(int)str[i]];

        if (d != -1) 
        {
            switch (phase) 
            {
            case 0:
                ++phase;
                break;
            case 1:
                c = ((prev_d << 2) | ((d & 0x30) >> 4));
                data.push_back(c);
                ++phase;
                break;
            case 2:
                c = (((prev_d & 0xf) << 4) | ((d & 0x3c) >> 2));
                data.push_back(c);
                ++phase;
                break;
            case 3:
                c = (((prev_d & 0x03) << 6) | d);
                data.push_back(c);
                phase = 0;
                break;
            }
            prev_d = d;
        }
    }
    return data;
}