/* Copyright (c) 2017, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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#ifndef OPENSSL_HEADER_SSL_SPAN_H
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#define OPENSSL_HEADER_SSL_SPAN_H
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#include <openssl/base.h>
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#if !defined(BORINGSSL_NO_CXX)
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extern "C++" {
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#include <algorithm>
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#include <cstdlib>
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#include <type_traits>
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BSSL_NAMESPACE_BEGIN
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template <typename T> class Span;
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namespace internal
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{
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template <typename T> class SpanBase
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{
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// Put comparison operator implementations into a base class with const T, so
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// they can be used with any type that implicitly converts into a Span.
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static_assert(std::is_const<T>::value, "Span<T> must be derived from SpanBase<const T>");
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friend bool operator==(Span<T> lhs, Span<T> rhs)
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{
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// MSVC issues warning C4996 because std::equal is unsafe. The pragma to
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// suppress the warning mysteriously has no effect, hence this
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// implementation. See
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// https://msdn.microsoft.com/en-us/library/aa985974.aspx.
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if (lhs.size() != rhs.size()) {
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return false;
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}
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for (T *l = lhs.begin(), *r = rhs.begin(); l != lhs.end() && r != rhs.end(); ++l, ++r) {
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if (*l != *r) {
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return false;
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}
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}
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return true;
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}
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friend bool operator!=(Span<T> lhs, Span<T> rhs)
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{
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return !(lhs == rhs);
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}
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};
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} // namespace internal
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// A Span<T> is a non-owning reference to a contiguous array of objects of type
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// |T|. Conceptually, a Span is a simple a pointer to |T| and a count of
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// elements accessible via that pointer. The elements referenced by the Span can
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// be mutated if |T| is mutable.
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//
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// A Span can be constructed from container types implementing |data()| and
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// |size()| methods. If |T| is constant, construction from a container type is
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// implicit. This allows writing methods that accept data from some unspecified
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// container type:
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//
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// // Foo views data referenced by v.
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// void Foo(bssl::Span<const uint8_t> v) { ... }
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//
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// std::vector<uint8_t> vec;
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// Foo(vec);
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//
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// For mutable Spans, conversion is explicit:
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//
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// // FooMutate mutates data referenced by v.
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// void FooMutate(bssl::Span<uint8_t> v) { ... }
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//
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// FooMutate(bssl::Span<uint8_t>(vec));
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//
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// You can also use the |MakeSpan| and |MakeConstSpan| factory methods to
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// construct Spans in order to deduce the type of the Span automatically.
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//
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// FooMutate(bssl::MakeSpan(vec));
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//
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// Note that Spans have value type sematics. They are cheap to construct and
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// copy, and should be passed by value whenever a method would otherwise accept
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// a reference or pointer to a container or array.
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template <typename T> class Span : private internal::SpanBase<const T>
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{
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private:
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// Heuristically test whether C is a container type that can be converted into
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// a Span by checking for data() and size() member functions.
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//
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// TODO(davidben): Switch everything to std::enable_if_t when we remove
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// support for MSVC 2015. Although we could write our own enable_if_t and MSVC
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// 2015 has std::enable_if_t anyway, MSVC 2015's SFINAE implementation is
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// problematic and does not work below unless we write the ::type at use.
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template <typename C>
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using EnableIfContainer = std::enable_if<std::is_convertible<decltype(std::declval<C>().data()), T*>::value &&
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std::is_integral<decltype(std::declval<C>().size())>::value>;
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static const size_t npos = static_cast<size_t>(-1);
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public:
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constexpr Span() : Span(nullptr, 0)
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{
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}
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constexpr Span(T* ptr, size_t len) : data_(ptr), size_(len)
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{
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}
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template <size_t N> constexpr Span(T (&array)[N]) : Span(array, N)
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{
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}
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template <typename C, typename = typename EnableIfContainer<C>::type,
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typename = typename std::enable_if<std::is_const<T>::value, C>::type>
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Span(const C& container) : data_(container.data()), size_(container.size())
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{
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}
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template <typename C, typename = typename EnableIfContainer<C>::type,
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typename = typename std::enable_if<!std::is_const<T>::value, C>::type>
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explicit Span(C& container) : data_(container.data()), size_(container.size())
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{
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}
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T* data() const
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{
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return data_;
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}
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size_t size() const
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{
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return size_;
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}
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bool empty() const
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{
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return size_ == 0;
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}
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T* begin() const
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{
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return data_;
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}
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const T* cbegin() const
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{
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return data_;
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}
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T* end() const
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{
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return data_ + size_;
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}
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const T* cend() const
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{
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return end();
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}
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T& front() const
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{
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if (size_ == 0) {
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abort();
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}
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return data_[0];
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}
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T& back() const
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{
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if (size_ == 0) {
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abort();
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}
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return data_[size_ - 1];
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}
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T& operator[](size_t i) const
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{
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if (i >= size_) {
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abort();
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}
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return data_[i];
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}
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T& at(size_t i) const
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{
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return (*this)[i];
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}
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Span subspan(size_t pos = 0, size_t len = npos) const
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{
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if (pos > size_) {
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abort(); // absl::Span throws an exception here.
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}
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return Span(data_ + pos, std::min(size_ - pos, len));
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}
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private:
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T* data_;
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size_t size_;
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};
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template <typename T> const size_t Span<T>::npos;
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template <typename T> Span<T> MakeSpan(T* ptr, size_t size)
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{
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return Span<T>(ptr, size);
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}
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template <typename C> auto MakeSpan(C& c) -> decltype(MakeSpan(c.data(), c.size()))
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{
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return MakeSpan(c.data(), c.size());
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}
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template <typename T> Span<const T> MakeConstSpan(T* ptr, size_t size)
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{
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return Span<const T>(ptr, size);
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}
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template <typename C> auto MakeConstSpan(const C& c) -> decltype(MakeConstSpan(c.data(), c.size()))
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{
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return MakeConstSpan(c.data(), c.size());
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}
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BSSL_NAMESPACE_END
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} // extern C++
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#endif // !defined(BORINGSSL_NO_CXX)
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#endif // OPENSSL_HEADER_SSL_SPAN_H
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