60 lines
2.9 KiB
C++
60 lines
2.9 KiB
C++
// Copyright (c) 2018 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_SPAN_H
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#define BITCOIN_SPAN_H
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#include <type_traits>
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#include <cstddef>
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#include <algorithm>
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/** A Span is an object that can refer to a contiguous sequence of objects.
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*
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* It implements a subset of C++20's std::span.
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*/
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template<typename C>
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class Span
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{
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C* m_data;
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std::ptrdiff_t m_size;
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public:
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constexpr Span() noexcept : m_data(nullptr), m_size(0) {}
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constexpr Span(C* data, std::ptrdiff_t size) noexcept : m_data(data), m_size(size) {}
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constexpr Span(C* data, C* end) noexcept : m_data(data), m_size(end - data) {}
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constexpr C* data() const noexcept { return m_data; }
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constexpr C* begin() const noexcept { return m_data; }
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constexpr C* end() const noexcept { return m_data + m_size; }
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constexpr std::ptrdiff_t size() const noexcept { return m_size; }
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constexpr C& operator[](std::ptrdiff_t pos) const noexcept { return m_data[pos]; }
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constexpr Span<C> subspan(std::ptrdiff_t offset) const noexcept { return Span<C>(m_data + offset, m_size - offset); }
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constexpr Span<C> subspan(std::ptrdiff_t offset, std::ptrdiff_t count) const noexcept { return Span<C>(m_data + offset, count); }
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constexpr Span<C> first(std::ptrdiff_t count) const noexcept { return Span<C>(m_data, count); }
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constexpr Span<C> last(std::ptrdiff_t count) const noexcept { return Span<C>(m_data + m_size - count, count); }
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friend constexpr bool operator==(const Span& a, const Span& b) noexcept { return a.size() == b.size() && std::equal(a.begin(), a.end(), b.begin()); }
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friend constexpr bool operator!=(const Span& a, const Span& b) noexcept { return !(a == b); }
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friend constexpr bool operator<(const Span& a, const Span& b) noexcept { return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end()); }
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friend constexpr bool operator<=(const Span& a, const Span& b) noexcept { return !(b < a); }
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friend constexpr bool operator>(const Span& a, const Span& b) noexcept { return (b < a); }
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friend constexpr bool operator>=(const Span& a, const Span& b) noexcept { return !(a < b); }
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};
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/** Create a span to a container exposing data() and size().
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*
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* This correctly deals with constness: the returned Span's element type will be
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* whatever data() returns a pointer to. If either the passed container is const,
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* or its element type is const, the resulting span will have a const element type.
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*
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* std::span will have a constructor that implements this functionality directly.
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*/
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template<typename A, int N>
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constexpr Span<A> MakeSpan(A (&a)[N]) { return Span<A>(a, N); }
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template<typename V>
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constexpr Span<typename std::remove_pointer<decltype(std::declval<V>().data())>::type> MakeSpan(V& v) { return Span<typename std::remove_pointer<decltype(std::declval<V>().data())>::type>(v.data(), v.size()); }
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#endif
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