SimpleYggGen-CPP/dev/cppcodec/detail/stream_codec.hpp

/**
 *  Copyright (C) 2015 Topology LP
 *  Copyright (C) 2018 Jakob Petsovits
 *  All rights reserved.
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to
 *  deal in the Software without restriction, including without limitation the
 *  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 *  sell copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 *  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 *  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 *  IN THE SOFTWARE.
 */

#ifndef CPPCODEC_DETAIL_STREAM_CODEC
#define CPPCODEC_DETAIL_STREAM_CODEC

#include <limits>
#include <stdlib.h> // for abort()
#include <stdint.h>

#include "../parse_error.hpp"
#include "config.hpp"

namespace cppcodec {
namespace detail {

using alphabet_index_t = uint_fast16_t;

template <typename Codec, typename CodecVariant>
class stream_codec
{
public:
    template <typename Result, typename ResultState> static void encode(
            Result& encoded_result, ResultState&, const uint8_t* binary, size_t binary_size);

    template <typename Result, typename ResultState> static void decode(
            Result& binary_result, ResultState&, const char* encoded, size_t encoded_size);

    static constexpr size_t encoded_size(size_t binary_size) noexcept;
    static constexpr size_t decoded_max_size(size_t encoded_size) noexcept;
};

template <bool GeneratesPadding> // default for CodecVariant::generates_padding() == false
struct padder {
    template <typename CodecVariant, typename Result, typename ResultState, typename EncodedBlockSizeT>
    CPPCODEC_ALWAYS_INLINE void operator()(Result&, ResultState&, EncodedBlockSizeT) { }
};

/* 
 * Почему закомментировано?

	template<> // specialization for CodecVariant::generates_padding() == true
	struct padder<true> {
		template <typename CodecVariant, typename Result, typename ResultState, typename EncodedBlockSizeT>
		CPPCODEC_ALWAYS_INLINE void operator()(
				Result& encoded, ResultState& state, EncodedBlockSizeT num_padding_characters)
		{
			for (EncodedBlockSizeT i = 0; i < num_padding_characters; ++i) {
				data::put(encoded, state, CodecVariant::padding_symbol());
			}
		}
	};
	
 * Потому что паддинги (знаки '=') в конце мешнейма нам не нужны. 
 * И вообще, как ты добрался сюда? 
 * С любовью из 2020, acetone.
*/ 

template <size_t I>
struct enc {
    // Block encoding: Go from 0 to (block size - 1), append a symbol for each iteration unconditionally.
    template <typename Codec, typename CodecVariant, typename Result, typename ResultState>
    static CPPCODEC_ALWAYS_INLINE void block(Result& encoded, ResultState& state, const uint8_t* src)
    {
        using EncodedBlockSizeT = decltype(Codec::encoded_block_size());
        constexpr static const EncodedBlockSizeT SymbolIndex = static_cast<EncodedBlockSizeT>(I - 1);

        enc<I - 1>().template block<Codec, CodecVariant>(encoded, state, src);
        data::put(encoded, state, CodecVariant::symbol(Codec::template index<SymbolIndex>(src)));
    }

    // Tail encoding: Go from 0 until (runtime) num_symbols, append a symbol for each iteration.
    template <typename Codec, typename CodecVariant, typename Result, typename ResultState,
            typename EncodedBlockSizeT = decltype(Codec::encoded_block_size())>
    static CPPCODEC_ALWAYS_INLINE void tail(
            Result& encoded, ResultState& state, const uint8_t* src, EncodedBlockSizeT num_symbols)
    {
        constexpr static const EncodedBlockSizeT SymbolIndex = Codec::encoded_block_size() - I;
        constexpr static const EncodedBlockSizeT NumSymbols = SymbolIndex + static_cast<EncodedBlockSizeT>(1);

        if (num_symbols == NumSymbols) {
            data::put(encoded, state, CodecVariant::symbol(Codec::template index_last<SymbolIndex>(src)));
            padder<CodecVariant::generates_padding()> pad;
#ifdef _MSC_VER
            pad.operator()<CodecVariant>(encoded, state, Codec::encoded_block_size() - NumSymbols);
#else
            pad.template operator()<CodecVariant>(encoded, state, Codec::encoded_block_size() - NumSymbols);
#endif
            return;
        }
        data::put(encoded, state, CodecVariant::symbol(Codec::template index<SymbolIndex>(src)));
        enc<I - 1>().template tail<Codec, CodecVariant>(encoded, state, src, num_symbols);
    }
};

template<> // terminating specialization
struct enc<0> {
    template <typename Codec, typename CodecVariant, typename Result, typename ResultState>
    static CPPCODEC_ALWAYS_INLINE void block(Result&, ResultState&, const uint8_t*) { }

    template <typename Codec, typename CodecVariant, typename Result, typename ResultState,
            typename EncodedBlockSizeT = decltype(Codec::encoded_block_size())>
    static CPPCODEC_ALWAYS_INLINE void tail(Result&, ResultState&, const uint8_t*, EncodedBlockSizeT)
    {
        abort(); // Not reached: block() should be called if num_symbols == block size, not tail().
    }
};

template <typename Codec, typename CodecVariant>
template <typename Result, typename ResultState>
inline void stream_codec<Codec, CodecVariant>::encode(
        Result& encoded_result, ResultState& state,
        const uint8_t* src, size_t src_size)
{
    using encoder = enc<Codec::encoded_block_size()>;

    const uint8_t* src_end = src + src_size;

    if (src_size >= Codec::binary_block_size()) {
        src_end -= Codec::binary_block_size();

        for (; src <= src_end; src += Codec::binary_block_size()) {
            encoder::template block<Codec, CodecVariant>(encoded_result, state, src);
        }
        src_end += Codec::binary_block_size();
    }

    if (src_end > src) {
        auto remaining_src_len = src_end - src;
        if (!remaining_src_len || remaining_src_len >= Codec::binary_block_size()) {
            abort();
            return;
        }
        auto num_symbols = Codec::num_encoded_tail_symbols(static_cast<uint8_t>(remaining_src_len));
        encoder::template tail<Codec, CodecVariant>(encoded_result, state, src, num_symbols);
    }
}

// Range & lookup table generation, see
// http://stackoverflow.com/questions/13313980/populate-an-array-using-constexpr-at-compile-time
// and http://cplusadd.blogspot.ca/2013/02/c11-compile-time-lookup-tablearray-with.html

template<unsigned... Is> struct seq {};

template<unsigned N, unsigned... Is>
struct gen_seq : gen_seq<N - 4, N - 4, N - 3, N - 2, N - 1, Is...> {
    // Clang up to 3.6 has a limit of 256 for template recursion,
    // so pass a few more symbols at once to make it work.
    static_assert(N % 4 == 0, "I must be divisible by 4 to eventually end at 0");
};
template<unsigned... Is>
struct gen_seq<0, Is...> : seq<Is...> {};

template <size_t N>
struct lookup_table_t {
    alphabet_index_t lookup[N];
    static constexpr size_t size = N;
};

template<typename LambdaType, unsigned... Is>
constexpr lookup_table_t<sizeof...(Is)> make_lookup_table(seq<Is...>, LambdaType value_for_index) {
    return { { value_for_index(Is)... } };
}

template<unsigned N, typename LambdaType>
constexpr lookup_table_t<N> make_lookup_table(LambdaType evalFunc) {
    return make_lookup_table(gen_seq<N>(), evalFunc);
}

// CodecVariant::symbol() provides a symbol for an index.
// Use recursive templates to get the inverse lookup table for fast decoding.

template <typename T>
static CPPCODEC_ALWAYS_INLINE constexpr size_t num_possible_values()
{
    return static_cast<size_t>(
            static_cast<intmax_t>(std::numeric_limits<T>::max())
                    - static_cast<intmax_t>(std::numeric_limits<T>::min()) + 1);
}

template <typename CodecVariant, alphabet_index_t InvalidIdx, size_t I>
struct index_if_in_alphabet {
    static CPPCODEC_ALWAYS_INLINE constexpr alphabet_index_t for_symbol(char symbol)
    {
        return (CodecVariant::symbol(
                    static_cast<alphabet_index_t>(CodecVariant::alphabet_size() - I)) == symbol)
            ? static_cast<alphabet_index_t>(CodecVariant::alphabet_size() - I)
            : index_if_in_alphabet<CodecVariant, InvalidIdx, I - 1>::for_symbol(symbol);
    }
};
template <typename CodecVariant, alphabet_index_t InvalidIdx>
struct index_if_in_alphabet<CodecVariant, InvalidIdx, 0> { // terminating specialization
    static CPPCODEC_ALWAYS_INLINE constexpr alphabet_index_t for_symbol(char)
    {
        return InvalidIdx;
    }
};

template <typename CodecVariant, size_t I>
struct padding_searcher {
    static CPPCODEC_ALWAYS_INLINE constexpr bool exists_padding_symbol()
    {
        // Clang up to 3.6 has a limit of 256 for template recursion,
        // so pass a few more symbols at once to make it work.
        static_assert(I % 4 == 0, "I must be divisible by 4 to eventually end at 0");

        return CodecVariant::is_padding_symbol(
                        static_cast<char>(num_possible_values<char>() - I - 4))
                || CodecVariant::is_padding_symbol(
                        static_cast<char>(num_possible_values<char>() - I - 3))
                || CodecVariant::is_padding_symbol(
                        static_cast<char>(num_possible_values<char>() - I - 2))
                || CodecVariant::is_padding_symbol(
                        static_cast<char>(num_possible_values<char>() - I - 1))
                || padding_searcher<CodecVariant, I - 4>::exists_padding_symbol();
    }
};
template <typename CodecVariant>
struct padding_searcher<CodecVariant, 0> { // terminating specialization
    static CPPCODEC_ALWAYS_INLINE constexpr bool exists_padding_symbol() { return false; }
};

template <typename CodecVariant>
struct alphabet_index_info
{
    static constexpr const size_t num_possible_symbols = num_possible_values<char>();

    static constexpr const alphabet_index_t padding_idx = 1 << 8;
    static constexpr const alphabet_index_t invalid_idx = 1 << 9;
    static constexpr const alphabet_index_t eof_idx = 1 << 10;
    static constexpr const alphabet_index_t stop_character_mask = static_cast<alphabet_index_t>(~0xFFu);

    static constexpr const bool padding_allowed = padding_searcher<
            CodecVariant, num_possible_symbols>::exists_padding_symbol();

    static CPPCODEC_ALWAYS_INLINE constexpr bool allows_padding()
    {
        return padding_allowed;
    }
    static CPPCODEC_ALWAYS_INLINE constexpr bool is_padding(alphabet_index_t idx)
    {
        return allows_padding() ? (idx == padding_idx) : false;
    }
    static CPPCODEC_ALWAYS_INLINE constexpr bool is_invalid(alphabet_index_t idx) { return idx == invalid_idx; }
    static CPPCODEC_ALWAYS_INLINE constexpr bool is_eof(alphabet_index_t idx) { return idx == eof_idx; }
    static CPPCODEC_ALWAYS_INLINE constexpr bool is_stop_character(alphabet_index_t idx)
    {
        return (idx & stop_character_mask) != 0;
    }

private:
    static CPPCODEC_ALWAYS_INLINE constexpr
    alphabet_index_t valid_index_or(alphabet_index_t a, alphabet_index_t b)
    {
        return a == invalid_idx ? b : a;
    }

    using idx_if_in_alphabet = index_if_in_alphabet<
            CodecVariant, invalid_idx, CodecVariant::alphabet_size()>;

    static CPPCODEC_ALWAYS_INLINE constexpr alphabet_index_t index_of(char symbol)
    {
        return valid_index_or(idx_if_in_alphabet::for_symbol(symbol),
            CodecVariant::is_eof_symbol(symbol) ? eof_idx
            : CodecVariant::is_padding_symbol(symbol) ? padding_idx
            : invalid_idx);
    }

    // GCC <= 4.9 has a bug with retaining constexpr when passing a function pointer.
    // To get around this, we'll create a callable with operator() and pass that one.
    // Unfortunately, MSVC prior to VS 2017 (for MinSizeRel or Release builds)
    // chokes on this by compiling the project in 20 minutes instead of seconds.
    // So let's define two separate variants and remove the old GCC one whenever we
    // decide not to support GCC < 5.0 anymore.
#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
    struct index_at {
        CPPCODEC_ALWAYS_INLINE constexpr alphabet_index_t operator()(size_t symbol) const {
            return index_of(CodecVariant::normalized_symbol(static_cast<char>(symbol)));
        }
    };
#else
    static CPPCODEC_ALWAYS_INLINE constexpr alphabet_index_t index_at(size_t symbol)
    {
        return index_of(CodecVariant::normalized_symbol(static_cast<char>(symbol)));
    }
#endif

public:
    struct lookup {
        static CPPCODEC_ALWAYS_INLINE alphabet_index_t for_symbol(char symbol)
        {
#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
            static constexpr const auto t = make_lookup_table<num_possible_symbols>(index_at());
#else
            static constexpr const auto t = make_lookup_table<num_possible_symbols>(&index_at);
#endif
            static_assert(t.size == num_possible_symbols,
                    "lookup table must cover each possible (character) symbol");
            return t.lookup[static_cast<uint8_t>(symbol)];
        }
    };
};

//
// At long last! The actual decode/encode functions.

template <typename Codec, typename CodecVariant>
template <typename Result, typename ResultState>
inline void stream_codec<Codec, CodecVariant>::decode(
        Result& binary_result, ResultState& state,
        const char* src_encoded, size_t src_size)
{
    using alphabet_index_lookup = typename alphabet_index_info<CodecVariant>::lookup;
    const char* src = src_encoded;
    const char* src_end = src + src_size;

    alphabet_index_t alphabet_indexes[Codec::encoded_block_size()] = {};
    alphabet_indexes[0] = alphabet_index_info<CodecVariant>::eof_idx;

    alphabet_index_t* const alphabet_index_start = &alphabet_indexes[0];
    alphabet_index_t* const alphabet_index_end = &alphabet_indexes[Codec::encoded_block_size()];
    alphabet_index_t* alphabet_index_ptr = &alphabet_indexes[0];

    while (src < src_end) {
        if (CodecVariant::should_ignore(*src)) {
            ++src;
            continue;
        }
        *alphabet_index_ptr = alphabet_index_lookup::for_symbol(*src);
        if (alphabet_index_info<CodecVariant>::is_stop_character(*alphabet_index_ptr)) {
            break;
        }
        ++src;
        ++alphabet_index_ptr;

        if (alphabet_index_ptr == alphabet_index_end) {
            Codec::decode_block(binary_result, state, alphabet_indexes);
            alphabet_index_ptr = alphabet_index_start;
        }
    }

    if (alphabet_index_info<CodecVariant>::is_invalid(*alphabet_index_ptr)) {
        throw symbol_error(*src);
    }
    ++src;

    alphabet_index_t* last_index_ptr = alphabet_index_ptr;
    if (alphabet_index_info<CodecVariant>::is_padding(*last_index_ptr)) {
        if (last_index_ptr == alphabet_index_start) {
            // Don't accept padding at the start of a block.
            // The encoder should have omitted that padding altogether.
            throw padding_error();
        }
        // We're in here because we just read a (first) padding character. Try to read more.
        // Count with last_index_ptr, but store in alphabet_index_ptr so we don't
        // overflow the array in case the input data is too long.
        ++last_index_ptr;
        while (src < src_end) {
            *alphabet_index_ptr = alphabet_index_lookup::for_symbol(*(src++));

            if (alphabet_index_info<CodecVariant>::is_eof(*alphabet_index_ptr)) {
                *alphabet_index_ptr = alphabet_index_info<CodecVariant>::padding_idx;
                break;
            }
            if (!alphabet_index_info<CodecVariant>::is_padding(*alphabet_index_ptr)) {
                throw padding_error();
            }

            ++last_index_ptr;
            if (last_index_ptr > alphabet_index_end) {
                throw padding_error();
            }
        }
    }

    if (last_index_ptr != alphabet_index_start)  {
        if ((CodecVariant::requires_padding()
                    || alphabet_index_info<CodecVariant>::is_padding(*alphabet_index_ptr)
                    ) && last_index_ptr != alphabet_index_end)
        {
            // If the input is not a multiple of the block size then the input is incorrect.
            throw padding_error();
        }
        if (alphabet_index_ptr >= alphabet_index_end) {
            abort();
            return;
        }
        Codec::decode_tail(binary_result, state, alphabet_indexes,
                static_cast<size_t>(alphabet_index_ptr - alphabet_index_start));
    }
}

template <typename Codec, typename CodecVariant>
inline constexpr size_t stream_codec<Codec, CodecVariant>::encoded_size(size_t binary_size) noexcept
{
    using C = Codec;

    // constexpr rules make this a lot harder to read than it actually is.
    return CodecVariant::generates_padding()
            // With padding, the encoded size is a multiple of the encoded block size.
            // To calculate that, round the binary size up to multiple of the binary block size,
            // then convert to encoded by multiplying with { base32: 8/5, base64: 4/3 }.
            ? (binary_size + (C::binary_block_size() - 1)
                    - ((binary_size + (C::binary_block_size() - 1)) % C::binary_block_size()))
                    * C::encoded_block_size() / C::binary_block_size()
            // No padding: only pad to the next multiple of 5 bits, i.e. at most a single extra byte.
            : (binary_size * C::encoded_block_size() / C::binary_block_size())
                    + (((binary_size * C::encoded_block_size()) % C::binary_block_size()) ? 1 : 0);
}

template <typename Codec, typename CodecVariant>
inline constexpr size_t stream_codec<Codec, CodecVariant>::decoded_max_size(size_t encoded_size) noexcept
{
    using C = Codec;

    return CodecVariant::requires_padding()
            ? (encoded_size / C::encoded_block_size() * C::binary_block_size())
            : (encoded_size / C::encoded_block_size() * C::binary_block_size())
                    + ((encoded_size % C::encoded_block_size())
                            * C::binary_block_size() / C::encoded_block_size());
}

} // namespace detail
} // namespace cppcodec

#endif // CPPCODEC_DETAIL_STREAM_CODEC