base64.hpp

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#ifndef CODEX_BASE64_BASE64_H
#define CODEX_BASE64_BASE64_H
 
#include <algorithm>
#include <iterator>
#include <limits>
#include <string_view>
 
using namespace std::literals;
 
consteval char lut_idx(std::string_view lut, char c) {
    const auto p = lut.data();
    const auto n = static_cast<char>(lut.size());
    return static_cast<char>(std::distance(p, std::find(p, p + n, c)));
}
 
consteval auto gen_rlut(std::string_view lut) {
    std::array<char, std::numeric_limits<unsigned char>::max()> ret = {};
    for(std::size_t i = 0; i < ret.size(); ++i)
        ret[i] = lut_idx(lut, static_cast<char>(i));
    ret['='] = 0;
    return ret;
}
 
class Base64 {
    static constexpr auto lut =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"sv;
    static constexpr auto rlut = gen_rlut(lut);
public:
    static void encode(std::string_view src, char *dst);
    static char *decode(std::string_view src, char *dst);
};
 
#endif