rfc4648-afo/common.hpp at master · YexuanXiao/rfc4648-afo · GitHub

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#pragma once

#pragma push_macro("BIZWEN_EXPORT")
#undef BIZWEN_EXPORT

#if !defined(BIZWEN_MODULE)
#define BIZWEN_EXPORT

#include <climits>
#include <memory>      // std::to_address
#include <tuple>
#include <type_traits> // std::remove_reference

#else

#define BIZWEN_EXPORT export

#endif

static_assert(CHAR_BIT == 8);

namespace bizwen
{

BIZWEN_EXPORT enum class rfc4648_kind : unsigned char
{
    base64,
    base64_url,
    base32,
    base32_lower,
    base32_mixed,
    base32_hex,
    base32_hex_lower,
    base32_hex_mixed,
    base32_crockford,
    base32_crockford_lower,
    base32_crockford_mixed,
    base16,
    base16_lower,
    base16_mixed,
    hex = base16,
    hex_lower = base16_lower,
    hex_mixed = base16_mixed
};

namespace detail
{
template <typename T>
auto to_address_const(T t)
{
    auto ptr = std::to_address(t);
    using const_pointer = std::add_const_t<std::remove_reference_t<decltype(*t)>> *;
    return const_pointer(ptr);
}

inline constexpr auto get_family(rfc4648_kind Kind)
{
    if (Kind == rfc4648_kind::base64 || Kind == rfc4648_kind::base64_url)
        return rfc4648_kind::base64;
    if (Kind == rfc4648_kind::base16 || Kind == rfc4648_kind::base16_lower || Kind == rfc4648_kind::base16_mixed)
        return rfc4648_kind::base16;
    else
        return rfc4648_kind::base32;
}

using buf_ref = unsigned char (&)[4];
using sig_ref = unsigned char &;

} // namespace detail

namespace encode_impl
{
BIZWEN_EXPORT struct rfc4648_encode_fn;
}

namespace decode_impl
{
BIZWEN_EXPORT struct rfc4648_decode_fn;
}

BIZWEN_EXPORT template <typename End, typename Out>
struct rfc4648_decode_result
{
    End end;
    Out out;

    operator std::tuple<End &, Out &>() && noexcept
    {
        return {end, out};
    }
};

BIZWEN_EXPORT class rfc4648_context
{
    // 0 - 2 for base64 encode, buf_[0 - 2] is significant
    // 0 - 4 for base32 encode, buf_[0 - 4] is significant
    // base16 encoding does not need ctx
    // 0 - 4 for base64 decode, only buf_[0] is significant
    // 0 - 8 for base32 decode, only buf_[0] is significant
    // 0 - 2 for base16 decode, only buf_[0] is significant
    alignas(int) unsigned char sig_{};
    alignas(int) unsigned char buf_[4];

    friend encode_impl::rfc4648_encode_fn;
    friend decode_impl::rfc4648_decode_fn;
};

BIZWEN_EXPORT inline constexpr std::size_t rfc4648_encode_length(std::size_t input, rfc4648_kind kind = rfc4648_kind::base64) noexcept
{
    if (detail::get_family(kind) == rfc4648_kind::base64)
        return (input + 5) / 6 * 8;
    else if (detail::get_family(kind) == rfc4648_kind::base32)
        return (input + 4) / 5 * 8;
    else
        return (input + 3) / 4 * 8;
}

BIZWEN_EXPORT inline constexpr std::size_t rfc4648_decode_length(std::size_t input, rfc4648_kind kind = rfc4648_kind::base64) noexcept
{
    if (detail::get_family(kind) == rfc4648_kind::base64)
        return (input + 7) / 8 * 6;
    else if (detail::get_family(kind) == rfc4648_kind::base32)
        return (input + 7) / 8 * 5;
    else
        return (input + 7) / 8 * 4;
}

} // namespace bizwen

#pragma pop_macro("BIZWEN_EXPORT")