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+/**
+ *  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_DATA_ACCESS
+#define CPPCODEC_DETAIL_DATA_ACCESS
+
+#include <stdint.h> // for size_t
+#include <string> // for static_assert() checking that string will be optimized
+#include <type_traits> // for std::enable_if, std::remove_reference, and such
+#include <utility> // for std::declval
+#include <vector> // for static_assert() checking that vector will be optimized
+
+#include "../detail/config.hpp" // for CPPCODEC_ALWAYS_INLINE
+
+namespace cppcodec {
+namespace data {
+
+// This file contains a number of templated data accessors that can be
+// implemented in the cppcodec::data namespace for types that don't fulfill
+// the default type requirements:
+// For result types: init(Result&, ResultState&, size_t capacity),
+//     put(Result&, ResultState&, char), finish(Result&, State&)
+// For const (read-only) types: char_data(const T&)
+// For both const and result types: size(const T&)
+
+template <typename T>
+CPPCODEC_ALWAYS_INLINE size_t size(const T& t) { return t.size(); }
+
+template <typename T, size_t N>
+CPPCODEC_ALWAYS_INLINE constexpr size_t size(const T (&t)[N]) noexcept {
+    return (void)t, N * sizeof(t[0]);
+}
+
+class general_t {};
+class specific_t : public general_t {};
+
+class empty_result_state {
+    template <typename Result>
+    CPPCODEC_ALWAYS_INLINE void size(const Result& result) { return size(result); }
+};
+
+// SFINAE: Generic fallback in case no specific state function applies.
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE empty_result_state create_state(Result&, general_t)
+{
+    return empty_result_state();
+}
+
+//
+// Generic templates for containers: Use these init()/put()/finish()
+// implementations if no specialization was found.
+//
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void init(Result& result, empty_result_state&, size_t capacity)
+{
+    result.resize(0);
+    result.reserve(capacity);
+}
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void finish(Result&, empty_result_state&)
+{
+    // Default is to push_back(), which already increases the size.
+}
+
+// For the put() default implementation, we try calling push_back() with either uint8_t or char,
+// whichever compiles. Scary-fancy template magic from http://stackoverflow.com/a/1386390.
+namespace fallback {
+    struct flag { char c[2]; }; // sizeof > 1
+    flag put_uint8(...);
+
+    int operator,(flag, flag);
+    template <typename T> void operator,(flag, T&); // map everything else to void
+    char operator,(int, flag); // sizeof 1
+}
+
+template <typename Result> inline void put_uint8(Result& result, uint8_t c) { result.push_back(c); }
+
+template <bool> struct put_impl;
+template <> struct put_impl<true> { // put_uint8() available
+    template<typename Result>
+    static CPPCODEC_ALWAYS_INLINE void put(Result& result, uint8_t c)
+    {
+        put_uint8(result, c);
+    }
+};
+template <> struct put_impl<false> { // put_uint8() not available
+    template<typename Result>
+    static CPPCODEC_ALWAYS_INLINE void put(Result& result, uint8_t c)
+    {
+        result.push_back(static_cast<char>(c));
+    }
+};
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void put(Result& result, empty_result_state&, uint8_t c)
+{
+    using namespace fallback;
+    put_impl<sizeof(fallback::flag(), put_uint8(result, c), fallback::flag()) != 1>::put(result, c);
+}
+
+//
+// Specialization for container types with direct mutable data access,
+// e.g. std::vector<uint8_t>.
+//
+// The expected way to specialize is to draft a new xyz_result_state type and
+// return an instance of it from a create_state() template specialization.
+// You can then create overloads for init(), put() and finish()
+// for the new result state type.
+//
+// If desired, a non-templated overload for both specific types
+// (result & state) can be added to tailor it to that particular result type.
+//
+
+template <typename T>
+constexpr auto data_is_mutable(T* t) -> decltype(t->data()[size_t(0)] = 'x', bool())
+{
+    return (void)t, true;
+}
+constexpr bool data_is_mutable(...) { return false; }
+
+template <typename Result>
+class direct_data_access_result_state
+{
+public:
+    CPPCODEC_ALWAYS_INLINE void init(Result& result, size_t capacity)
+    {
+        // reserve() may not actually allocate the storage right away,
+        // and it isn't guaranteed that it will be untouched upon the
+        //.next resize(). In that light, resize from the start and
+        // slightly reduce the size at the end if necessary.
+        result.resize(capacity);
+
+        // result.data() may perform a calculation to retrieve the address.
+        // E.g. std::string (since C++11) will use small string optimization,
+        // so it needs to check if it's using allocated data or (ab)using
+        // its own member variables interpreted as char array.
+        // (This result_state is used for std::string starting with C++17.)
+        // Conditional code paths are slow so we only do it once, at the start.
+        m_buffer = result.data();
+    }
+    CPPCODEC_ALWAYS_INLINE void put(Result&, char c)
+    {
+        m_buffer[m_offset++] = c;
+    }
+    CPPCODEC_ALWAYS_INLINE void finish(Result& result)
+    {
+        result.resize(m_offset);
+    }
+    CPPCODEC_ALWAYS_INLINE size_t size(const Result&)
+    {
+        return m_offset;
+    }
+private:
+    // Make sure to get the mutable buffer decltype by using assignment.
+    typename std::remove_reference<
+            decltype(std::declval<Result>().data()[size_t(0)] = 'x')>::type* m_buffer;
+    size_t m_offset = 0;
+};
+
+// SFINAE: Select a specific state based on the result type and possible result state type.
+// Implement this if direct data access (`result.data()[0] = 'x') isn't already possible
+// and you want to specialize it for your own result type.
+// Note: The enable_if should ideally be part of the class declaration,
+//       but Visual Studio C++ will not compile it that way.
+//       Have it here in the factory function instead.
+template <typename Result,
+          typename = typename std::enable_if<
+                  data_is_mutable(static_cast<Result*>(nullptr))>::type>
+CPPCODEC_ALWAYS_INLINE direct_data_access_result_state<Result> create_state(Result&, specific_t)
+{
+    return direct_data_access_result_state<Result>();
+}
+
+static_assert(std::is_same<
+        decltype(create_state(*static_cast<std::vector<uint8_t>*>(nullptr), specific_t())),
+        direct_data_access_result_state<std::vector<uint8_t>>>::value,
+        "std::vector<uint8_t> must be handled by direct_data_access_result_state");
+
+// Specialized init(), put() and finish() functions for direct_data_access_result_state.
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void init(Result& result, direct_data_access_result_state<Result>& state, size_t capacity)
+{
+    state.init(result, capacity);
+}
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void put(Result& result, direct_data_access_result_state<Result>& state, char c)
+{
+    state.put(result, c);
+}
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void finish(Result& result, direct_data_access_result_state<Result>& state)
+{
+    state.finish(result);
+}
+
+//
+// Specialization for container types with direct mutable array access,
+// e.g. std::string. This is generally faster because bound checks are
+// minimal and operator[] is more likely noexcept. In addition,
+// std::string::push_back() needs to write a null character on every
+// expansion, which should be more efficient when done in bulk by resize().
+//
+// Compared to the above, tracking an extra offset variable is cheap.
+//
+
+template <typename T>
+constexpr auto array_access_is_mutable(T* t) -> decltype((*t)[size_t(0)] = 'x', bool())
+{
+    return (void)t, true;
+}
+constexpr bool array_access_is_mutable(...) { return false; }
+
+template <typename Result>
+class array_access_result_state
+{
+public:
+    CPPCODEC_ALWAYS_INLINE void init(Result& result, size_t capacity)
+    {
+        // reserve() may not actually allocate the storage right away,
+        // and it isn't guaranteed that it will be untouched upon the
+        //.next resize(). In that light, resize from the start and
+        // slightly reduce the size at the end if necessary.
+        result.resize(capacity);
+    }
+    CPPCODEC_ALWAYS_INLINE void put(Result& result, char c)
+    {
+        result[m_offset++] = c;
+    }
+    CPPCODEC_ALWAYS_INLINE void finish(Result& result)
+    {
+        result.resize(m_offset);
+    }
+    CPPCODEC_ALWAYS_INLINE size_t size(const Result&)
+    {
+        return m_offset;
+    }
+private:
+    size_t m_offset = 0;
+};
+
+// SFINAE: Select a specific state based on the result type and possible result state type.
+// Note: The enable_if should ideally be part of the class declaration,
+//       but Visual Studio C++ will not compile it that way.
+//       Have it here in the factory function instead.
+template <typename Result,
+          typename = typename std::enable_if<
+                  !data_is_mutable(static_cast<Result*>(nullptr)) // no more than one template option
+                  && array_access_is_mutable(static_cast<Result*>(nullptr))>::type>
+CPPCODEC_ALWAYS_INLINE array_access_result_state<Result> create_state(Result&, specific_t)
+{
+    return array_access_result_state<Result>();
+}
+
+#if __cplusplus >= 201703L || (defined(_MSVC_LANG) && _MSVC_LANG > 201703L)
+static_assert(std::is_same<
+    decltype(create_state(*static_cast<std::string*>(nullptr), specific_t())),
+    direct_data_access_result_state<std::string>>::value,
+    "std::string (C++17 and later) must be handled by direct_data_access_result_state");
+#elif __cplusplus < 201703 && !defined(_MSVC_LANG) // we can't trust MSVC to set this right
+static_assert(std::is_same<
+        decltype(create_state(*static_cast<std::string*>(nullptr), specific_t())),
+        array_access_result_state<std::string>>::value,
+        "std::string (pre-C++17) must be handled by array_access_result_state");
+#endif
+
+// Specialized init(), put() and finish() functions for array_access_result_state.
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void init(Result& result, array_access_result_state<Result>& state, size_t capacity)
+{
+    state.init(result, capacity);
+}
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void put(Result& result, array_access_result_state<Result>& state, char c)
+{
+    state.put(result, c);
+}
+
+template <typename Result>
+CPPCODEC_ALWAYS_INLINE void finish(Result& result, array_access_result_state<Result>& state)
+{
+    state.finish(result);
+}
+
+// char_data() is only used to read, not for result buffers.
+template <typename T> inline const char* char_data(const T& t)
+{
+    return reinterpret_cast<const char*>(t.data());
+}
+template <typename T, size_t N> inline const char* char_data(const T (&t)[N]) noexcept
+{
+    return reinterpret_cast<const char*>(&(t[0]));
+}
+
+template <typename T> inline const uint8_t* uchar_data(const T& t)
+{
+    return reinterpret_cast<const uint8_t*>(char_data(t));
+}
+
+} // namespace data
+} // namespace cppcodec
+
+#endif