ncc/base64.cpp at main · Tsukuba-Programming-Lab/ncc · GitHub

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//
//  base64.cpp
//  ncc
//
//  Created by yuki on 2022/05/27.
//

#include "base64.hpp"


bool algorithm::encode_base64(const std::vector<unsigned char>& src, std::string& dst) {
    const std::string table("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");
    std::string       cdst;

    for (std::size_t i = 0; i < src.size(); ++i) {
        switch (i % 3) {
        case 0:
            cdst.push_back(table[(src[i] & 0xFC) >> 2]);
            if (i + 1 == src.size()) {
                cdst.push_back(table[(src[i] & 0x03) << 4]);
                cdst.push_back('=');
                cdst.push_back('=');
            }

            break;
        case 1:
            cdst.push_back(table[((src[i - 1] & 0x03) << 4) | ((src[i + 0] & 0xF0) >> 4)]);
            if (i + 1 == src.size()) {
                cdst.push_back(table[(src[i] & 0x0F) << 2]);
                cdst.push_back('=');
            }

            break;
        case 2:
            cdst.push_back(table[((src[i - 1] & 0x0F) << 2) | ((src[i + 0] & 0xC0) >> 6)]);
            cdst.push_back(table[src[i] & 0x3F]);

            break;
        }
    }

    dst.swap(cdst);

    return true;
}


// base64 デコード
bool algorithm::decode_base64(const std::string& src, std::vector<unsigned char>& dst)
{
    if (src.size() & 0x00000003) {
        return false;
    }
    else {
        const std::string          table("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");
        std::vector<unsigned char> cdst;

        for (std::size_t i = 0; i < src.size(); i += 4) {
            if (src[i + 0] == '=') {
                return false;
            }
            else if (src[i + 1] == '=') {
                return false;
            }
            else if (src[i + 2] == '=') {
                const std::string::size_type s1 = table.find(src[i + 0]);
                const std::string::size_type s2 = table.find(src[i + 1]);

                if (s1 == std::string::npos || s2 == std::string::npos) {
                    return false;
                }

                cdst.push_back(static_cast<unsigned char>(((s1 & 0x3F) << 2) | ((s2 & 0x30) >> 4)));

                break;
            }
            else if (src[i + 3] == '=') {
                const std::string::size_type s1 = table.find(src[i + 0]);
                const std::string::size_type s2 = table.find(src[i + 1]);
                const std::string::size_type s3 = table.find(src[i + 2]);

                if (s1 == std::string::npos || s2 == std::string::npos || s3 == std::string::npos) {
                    return false;
                }

                cdst.push_back(static_cast<unsigned char>(((s1 & 0x3F) << 2) | ((s2 & 0x30) >> 4)));
                cdst.push_back(static_cast<unsigned char>(((s2 & 0x0F) << 4) | ((s3 & 0x3C) >> 2)));

                break;
            }
            else {
                const std::string::size_type s1 = table.find(src[i + 0]);
                const std::string::size_type s2 = table.find(src[i + 1]);
                const std::string::size_type s3 = table.find(src[i + 2]);
                const std::string::size_type s4 = table.find(src[i + 3]);

                if (s1 == std::string::npos || s2 == std::string::npos || s3 == std::string::npos || s4 == std::string::npos) {
                    return false;
                }

                cdst.push_back(static_cast<unsigned char>(((s1 & 0x3F) << 2) | ((s2 & 0x30) >> 4)));
                cdst.push_back(static_cast<unsigned char>(((s2 & 0x0F) << 4) | ((s3 & 0x3C) >> 2)));
                cdst.push_back(static_cast<unsigned char>(((s3 & 0x03) << 6) | ((s4 & 0x3F) >> 0)));
            }
        }

        dst.swap(cdst);

        return true;
    }
}