mirror of
https://github.com/matrix-construct/construct
synced 2024-10-31 19:08:59 +01:00
403 lines
11 KiB
C++
403 lines
11 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
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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 is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_STRING_VIEW_H
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namespace ircd
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{
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struct string_view;
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constexpr size_t _constexpr_strlen(const char *) noexcept;
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template<size_t N> consteval size_t _constexpr_strlen(const char (&)[N]) noexcept;
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constexpr bool _constexpr_equal(const char *a, const char *b) noexcept;
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constexpr bool _constexpr_equal(const char *a, const char *b, size_t) noexcept;
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constexpr bool _constexpr_equal(const char *a, const size_t, const char *b, const size_t) noexcept;
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constexpr bool _constexpr_equal(const string_view &, const string_view &) noexcept;
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template<size_t N0, size_t N1> consteval bool _constexpr_equal(const char (&)[N0], const char (&)[N1]) noexcept;
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constexpr const char *data(const string_view &) noexcept;
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constexpr size_t size(const string_view &) noexcept;
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bool empty(const string_view &);
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bool operator!(const string_view &);
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bool defined(const string_view &);
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bool null(const string_view &);
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int cmp(const string_view &, const string_view &) noexcept;
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constexpr string_view operator ""_sv(const char *const literal, const size_t size);
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}
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namespace std
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{
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template<> struct std::hash<ircd::string_view>;
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template<> struct std::less<ircd::string_view>;
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template<> struct std::equal_to<ircd::string_view>;
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}
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/// Customized std::string_view (experimental TS / C++17)
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///
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/// This class adds iterator-based (char*, char*) construction to std::string_view which otherwise
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/// takes traditional (char*, size_t) arguments. This allows boost::spirit grammars to create
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/// string_view's using the raw[] directive achieving zero-copy/zero-allocation parsing.
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///
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struct ircd::string_view
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:std::string_view
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{
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// (non-standard)
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explicit operator bool() const
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{
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return !empty();
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}
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/// CAREFUL. THIS IS ON PURPOSE. By relaxing this conversion we're reducing
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/// the amount of explicit std::string() pollution when calling out to code
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/// which doesn't support string_view *yet* (keyword: yet). When it does
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/// support string_view then this conversion won't happen, and we don't
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/// have to change anything in our code. The price here is that an
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/// occasional regression analysis on where these conversions are occurring
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/// should be periodically performed to make sure there are no unwanted
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/// silent accidents.
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operator std::string() const
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{
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return std::string(cbegin(), cend());
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}
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/// (non-standard) When data() != nullptr we consider the string defined
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/// downstream in this project wrt JS/JSON. This is the bit of information
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/// we're deciding on for defined|undefined. If this string_view is
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/// constructed from a literal "" we must assert that inputs a valid pointer
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/// in the std::string_view with length 0; stdlib can't optimize that with
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/// a nullptr replacement.
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bool undefined() const
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{
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return data() == nullptr;
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}
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bool defined() const
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{
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return !undefined();
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}
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/// (non-standard) string_view's have no guarantee to be null terminated
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/// and most likely aren't. The std::string_view does not offer the
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/// c_str() function because using it is overwhelmingly likely to be wrong.
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/// Nevertheless if our developer is certain their view is of a null
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/// terminated string where the terminator is one past the end they can
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/// invoke this function rather than data() to assert their intent. Note
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/// that this assertion is still not foolproof because reading beyond
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/// size() might still be incorrect whether or not a null is found there
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/// and there is nothing else we can do. The developer must be sure.
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auto c_str() const
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{
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assert(!data() || data()[size()] == '\0');
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return data();
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}
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/// (non-standard) After using data() == nullptr for undefined, we're fresh
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/// out of legitimate bits here to represent the null type string. In this
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/// case we expect a hack pointer of 0x1 which will mean JS null
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bool null() const
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{
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return data() == reinterpret_cast<const char *>(0x1);
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}
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// (non-standard) Non-throwing substr() which returns empty rather than std::out_of_range.
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// This avoids generating numerous eh handlers/terminations/unwind blocks etc.
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using std::string_view::substr;
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constexpr auto substr(std::nothrow_t, size_t pos = 0, size_t count = npos) const noexcept
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{
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pos = std::min(pos, size());
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count = std::min(count, size() - pos);
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return std::string_view::substr(pos, count);
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}
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// (non-standard) our faux insert stub
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// Tricks boost::spirit into thinking this is mutable string (hint: it's not).
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// Instead, the raw[] directive in Qi grammar will use the iterator constructor only.
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// __attribute__((error("string_view is not insertable (hint: use raw[] directive)")))
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#if !defined(NDEBUG) && !defined(RB_ASSERT)
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[[noreturn]]
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#endif
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void insert(const iterator &, const char &)
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{
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assert(0);
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}
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// (non-standard) our iterator-based assign
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string_view &assign(const char *const &__restrict__ begin, const char *const &__restrict__ end)
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{
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this->~string_view();
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new (this) string_view{begin, end};
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return *this;
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}
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// (non-standard) intuitive wrapper for remove_suffix.
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// Unlike std::string, we can cheaply involve a reference to the removed character
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// which still exists.
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const char &pop_back()
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{
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const char &ret(back());
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remove_suffix(1);
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return ret;
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}
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// (non-standard) intuitive wrapper for remove_prefix.
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// Unlike std::string, we can cheaply involve a reference to the removed character
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// which still exists.
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const char &pop_front()
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{
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const char &ret(front());
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remove_prefix(1);
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return ret;
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}
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/// (non-standard) resize viewer
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void resize(const size_t &count)
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{
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*this = string_view{data(), data() + count};
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}
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// (non-standard) our iterator-based constructor
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constexpr string_view(const char *const &__restrict__ begin, const char *const &__restrict__ end) noexcept
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:string_view{begin, size_t(end - begin)}
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{
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assert(begin <= end);
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}
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// (non-standard) our iterator-based constructor
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string_view(const std::string::const_iterator &begin, const std::string::const_iterator &end)
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:string_view{&*begin, &*end}
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{}
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// (non-standard) our array based constructor
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template<size_t SIZE> constexpr
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__attribute__((always_inline))
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string_view(const std::array<char, SIZE> &array) noexcept
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:string_view
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{
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array.data(), std::find(array.begin(), array.end(), '\0')
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}{}
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// (non-standard) our buffer based constructor
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template<size_t SIZE> constexpr
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__attribute__((always_inline))
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string_view(const char (&__restrict__ buf)[SIZE]) noexcept
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:string_view
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{
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buf, std::find(buf, buf + SIZE, '\0')
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}{}
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constexpr string_view(const char *const &__restrict__ start, const size_t &size) noexcept
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:std::string_view{start, size}
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{}
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constexpr string_view(const char *const &__restrict__ start) noexcept
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:std::string_view{start, _constexpr_strlen(start)}
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{}
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string_view(std::string &&) noexcept = delete;
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string_view(const std::string &string) noexcept
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:string_view{string.data(), string.size()}
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{}
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constexpr string_view(const std::string_view &sv)
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:std::string_view{sv}
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{}
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/// Our default constructor sets the elements to 0 for best behavior by
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/// defined() and null() et al.
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constexpr string_view()
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:std::string_view{}
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{}
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};
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/// Specialization for std::hash<> participation
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template<>
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struct std::hash<ircd::string_view>
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:std::hash<std::string_view>
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{
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using std::hash<std::string_view>::operator();
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using std::hash<std::string_view>::hash;
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};
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/// Specialization for std::less<> participation
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template<>
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struct std::less<ircd::string_view>
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:std::less<std::string_view>
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{
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using std::less<std::string_view>::operator();
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using std::less<std::string_view>::less;
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};
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/// Specialization for std::equal_to<> participation
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template<>
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struct std::equal_to<ircd::string_view>
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:std::equal_to<std::string_view>
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{
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using std::equal_to<std::string_view>::operator();
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using std::equal_to<std::string_view>::equal_to;
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};
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/// Compile-time conversion from a string literal into a string_view.
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constexpr ircd::string_view
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ircd::operator ""_sv(const char *const literal, const size_t size)
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{
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return string_view{literal, size};
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}
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inline int
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ircd::cmp(const string_view &a,
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const string_view &b)
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noexcept
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{
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const auto res
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{
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#if __has_builtin(__builtin_memcmp_inline) && !defined(RB_GENERIC)
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__builtin_memcmp_inline(a.data(), b.data(), std::min(a.size(), b.size()))
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#else
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__builtin_memcmp(a.data(), b.data(), std::min(a.size(), b.size()))
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#endif
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};
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const auto zf
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{
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boolmask<uint>(res == 0)
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};
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const auto lt
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{
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boolmask<uint>(a.size() < b.size())
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};
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const auto gt
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{
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boolmask<uint>(a.size() > b.size())
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};
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return (~zf & res) | (zf & lt & -1U) | (zf & gt & 1U);
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}
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inline bool
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ircd::operator!(const string_view &str)
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{
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return empty(str);
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}
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inline bool
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ircd::empty(const string_view &str)
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{
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return str.empty();
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}
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inline bool
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ircd::null(const string_view &str)
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{
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return str.null();
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}
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inline bool
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ircd::defined(const string_view &str)
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{
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return str.defined();
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}
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constexpr size_t
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ircd::size(const string_view &str)
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noexcept
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{
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return str.size();
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}
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constexpr const char *
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ircd::data(const string_view &str)
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noexcept
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{
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return str.data();
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}
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template<size_t N0,
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size_t N1>
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consteval bool
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ircd::_constexpr_equal(const char (&a)[N0],
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const char (&b)[N1])
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noexcept
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{
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if constexpr(_constexpr_strlen(a) != _constexpr_strlen(b))
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return false;
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for(size_t i(0); i < _constexpr_strlen(a); ++i)
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if constexpr(a[i] != b[i])
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return false;
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return true;
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}
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constexpr bool
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ircd::_constexpr_equal(const string_view &a,
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const string_view &b)
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noexcept
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{
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if constexpr(__cplusplus >= 202002L)
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return a == b;
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else
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return _constexpr_equal(data(a), size(a), data(b), size(b));
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}
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constexpr bool
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ircd::_constexpr_equal(const char *const a,
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const size_t a_len,
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const char *const b,
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const size_t b_len)
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noexcept
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{
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return a_len == b_len && _constexpr_equal(a, b, a_len);
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}
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constexpr bool
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ircd::_constexpr_equal(const char *const a,
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const char *const b,
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size_t len)
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noexcept
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{
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return !len || (*a == *b && (*a == '\0' || _constexpr_equal(a + 1, b + 1, len - 1)));
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}
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constexpr bool
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ircd::_constexpr_equal(const char *const a,
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const char *const b)
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noexcept
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{
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return *a == *b && (*a == '\0' || _constexpr_equal(a + 1, b + 1));
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}
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template<size_t N>
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consteval size_t
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ircd::_constexpr_strlen(const char (&a)[N])
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noexcept
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{
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size_t i(0);
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while(i < N)
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if constexpr(a[i] == '\0')
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return i;
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return N;
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}
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constexpr size_t
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ircd::_constexpr_strlen(const char *const s)
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noexcept
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{
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const char *e(s);
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if(e) for(; *e; ++e);
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return e - s;
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}
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