177 lines
6.8 KiB
C++
177 lines
6.8 KiB
C++
// Copyright (c) 2017-2022, The Monero Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#pragma once
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#include <algorithm>
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#include <cstdint>
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#include <memory>
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#include <type_traits>
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namespace epee
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{
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/*!
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\brief Non-owning sequence of data. Does not deep copy
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Inspired by `gsl::span` and/or `boost::iterator_range`. This class is
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intended to be used as a parameter type for functions that need to take a
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writable or read-only sequence of data. Most common cases are `span<char>`
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and `span<std::uint8_t>`. Using as a class member is only recommended if
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clearly documented as not doing a deep-copy. C-arrays are easily convertible
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to this type.
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\note Conversion from C string literal to `span<const char>` will include
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the NULL-terminator.
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\note Never allows derived-to-base pointer conversion; an array of derived
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types is not an array of base types.
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*/
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template<typename T>
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class span
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{
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template<typename U>
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static constexpr bool safe_conversion() noexcept
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{
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// Allow exact matches or `T*` -> `const T*`.
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using with_const = typename std::add_const<U>::type;
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return std::is_same<T, U>() ||
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(std::is_const<T>() && std::is_same<T, with_const>());
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}
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public:
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using value_type = T;
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using size_type = std::size_t;
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using difference_type = std::ptrdiff_t;
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using pointer = T*;
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using const_pointer = const T*;
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using reference = T&;
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using const_reference = const T&;
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using iterator = pointer;
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using const_iterator = const_pointer;
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constexpr span() noexcept : ptr(nullptr), len(0) {}
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constexpr span(std::nullptr_t) noexcept : span() {}
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//! Prevent derived-to-base conversions; invalid in this context.
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template<typename U, typename = typename std::enable_if<safe_conversion<U>()>::type>
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constexpr span(U* const src_ptr, const std::size_t count) noexcept
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: ptr(src_ptr), len(count) {}
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//! Conversion from C-array. Prevents common bugs with sizeof + arrays.
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template<std::size_t N>
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constexpr span(T (&src)[N]) noexcept : span(src, N) {}
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constexpr span(const span&) noexcept = default;
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span& operator=(const span&) noexcept = default;
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/*! Try to remove `amount` elements from beginning of span.
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\return Number of elements removed. */
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std::size_t remove_prefix(std::size_t amount) noexcept
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{
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amount = std::min(len, amount);
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ptr += amount;
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len -= amount;
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return amount;
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}
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constexpr iterator begin() const noexcept { return ptr; }
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constexpr const_iterator cbegin() const noexcept { return ptr; }
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constexpr iterator end() const noexcept { return begin() + size(); }
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constexpr const_iterator cend() const noexcept { return cbegin() + size(); }
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constexpr bool empty() const noexcept { return size() == 0; }
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constexpr pointer data() const noexcept { return ptr; }
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constexpr std::size_t size() const noexcept { return len; }
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constexpr std::size_t size_bytes() const noexcept { return size() * sizeof(value_type); }
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T &operator[](size_t idx) noexcept { return ptr[idx]; }
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const T &operator[](size_t idx) const noexcept { return ptr[idx]; }
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private:
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T* ptr;
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std::size_t len;
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};
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//! \return `span<const T::value_type>` from a STL compatible `src`.
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template<typename T>
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constexpr span<const typename T::value_type> to_span(const T& src)
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{
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// compiler provides diagnostic if size() is not size_t.
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return {src.data(), src.size()};
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}
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//! \return `span<T::value_type>` from a STL compatible `src`.
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template<typename T>
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constexpr span<typename T::value_type> to_mut_span(T& src)
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{
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// compiler provides diagnostic if size() is not size_t.
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return {src.data(), src.size()};
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}
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template<typename T>
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constexpr bool has_padding() noexcept
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{
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return !std::is_standard_layout<T>() || alignof(T) != 1;
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}
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//! \return Cast data from `src` as `span<const std::uint8_t>`.
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template<typename T>
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span<const std::uint8_t> to_byte_span(const span<const T> src) noexcept
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{
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static_assert(!has_padding<T>(), "source type may have padding");
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return {reinterpret_cast<const std::uint8_t*>(src.data()), src.size_bytes()};
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}
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//! \return `span<const std::uint8_t>` which represents the bytes at `&src`.
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template<typename T>
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span<const std::uint8_t> as_byte_span(const T& src) noexcept
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{
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static_assert(!std::is_empty<T>(), "empty types will not work -> sizeof == 1");
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static_assert(!has_padding<T>(), "source type may have padding");
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return {reinterpret_cast<const std::uint8_t*>(std::addressof(src)), sizeof(T)};
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}
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//! \return `span<std::uint8_t>` which represents the bytes at `&src`.
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template<typename T>
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span<std::uint8_t> as_mut_byte_span(T& src) noexcept
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{
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static_assert(!std::is_empty<T>(), "empty types will not work -> sizeof == 1");
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static_assert(!has_padding<T>(), "source type may have padding");
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return {reinterpret_cast<std::uint8_t*>(std::addressof(src)), sizeof(T)};
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}
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//! make a span from a std::string
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template<typename T, typename U>
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span<const T> strspan(const U&s) noexcept
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{
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static_assert(std::is_same<typename U::value_type, char>(), "unexpected source type");
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static_assert(std::is_same<T, char>() || std::is_same<T, unsigned char>() || std::is_same<T, int8_t>() || std::is_same<T, uint8_t>(), "Unexpected destination type");
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return {reinterpret_cast<const T*>(s.data()), s.size()};
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}
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}
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