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◆ main openmsx / src / utils / ranges.hh
4.6 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef RANGES_HH
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#define RANGES_HH
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#include <algorithm>
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#include <bit>
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#include <cassert>
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#include <cstdint>
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#include <functional>
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#include <iterator>
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#include <memory>
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#include <ranges>
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#include <span>
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#include <version> // for _LIBCPP_VERSION
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// Range based versions of the standard algorithms, these will likely become
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// part of c++20. For example see this post:
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//   http://ericniebler.com/2018/12/05/standard-ranges/
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// In the future we can remove our implementation and instead use the standard
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// version (e.g. by a namespace alias like 'namespace ranges = std::ranges').
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//
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// All of the range algorithms below do nothing more than delegate to the
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// corresponding iterator-pair version of the algorithm.
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//
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// This list of algorithms is not complete. But it's easy to extend if/when we
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// need more.
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namespace ranges {
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// part of c++23, not yet available in clang-16
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template<std::forward_iterator ForwardIt, typename T>
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constexpr void iota(ForwardIt first, ForwardIt last, T value)
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{
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	while (first != last) {
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		*first++ = value;
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		++value;
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	}
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}
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template<std::ranges::forward_range Range, typename T>
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constexpr void iota(Range&& range, T&& value)
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{
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	::ranges::iota(std::ranges::begin(range), std::ranges::end(range), std::forward<T>(value));
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}
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// Test whether all elements in the given range are equal to each other (after
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// applying a projection).
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template<std::ranges::input_range Range, typename Proj = std::identity>
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bool all_equal(Range&& range, Proj proj = {})
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{
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	auto it = std::ranges::begin(range);
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	auto et = std::ranges::end(range);
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	if (it == et) return true;
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	auto val = std::invoke(proj, *it);
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	for (++it; it != et; ++it) {
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		if (std::invoke(proj, *it) != val) {
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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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} // namespace ranges
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// Copy from a (sized-)range to another (non-overlapping) (sized-)range.
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// This differs from std::ranges::copy() in how the destination is passed:
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// * This version requires a (sized-)range.
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// * std::ranges::copy() requires an output-iterator.
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// The latter is more general, but the former can do an extra safety check:
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// * The destination size must be as least as large as the source size.
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template<std::ranges::sized_range Input, std::ranges::sized_range Output>
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constexpr auto copy_to_range(Input&& in, Output&& out)
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{
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	assert(std::ranges::size(in) <= std::ranges::size(out));
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	// Workaround: this doesn't work when copying a std::initializer_list into a std::array with libstdc++ debug-STL ???
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	//     return std::copy(std::begin(in), std::end(in), std::begin(out));
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	auto f = std::ranges::begin(in);
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	auto l = std::ranges::end(in);
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	auto o = std::ranges::begin(out);
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	while (f != l) {
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		*o++ = *f++;
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	}
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	return o;
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}
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// Perform a binary-search in a sorted range.
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// The given 'range' must be sorted according to 'comp'.
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// We search for 'value' after applying 'proj' to the elements in the range.
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// Returns a pointer to the element in 'range', or nullptr if not found.
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//
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// This helper function is typically used to simplify code like:
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//     auto it = std::ranges::lower_bound(myMap, name, {}, &Element::name);
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//     if ((it != myMap.end()) && (it->name == name)) {
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//         ... use *it
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//     }
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// Note that this code needs to check both for the end-iterator and that the
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// element was actually found. By using binary_find() this complexity is hidden:
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//     if (auto m = binary_find(myMap, name, {}, &Element::name)) {
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//         ... use *m
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//     }
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template<std::ranges::forward_range Range, typename T, typename Compare = std::less<>, typename Proj = std::identity>
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[[nodiscard]] auto* binary_find(Range&& range, const T& value, Compare comp = {}, Proj proj = {})
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{
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	auto it = std::ranges::lower_bound(range, value, comp, proj);
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	return ((it != std::ranges::end(range)) && (!std::invoke(comp, value, std::invoke(proj, *it))))
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	       ? std::to_address(it)
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	       : nullptr;
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}
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// Convenience function to convert part of an array (or vector, ...) into a
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// span. These are not part of the c++ ranges namespace, but often these results
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// are then further used in range algorithms, that's why I placed them in this
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// header.
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template<std::ranges::range Range>
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[[nodiscard]] constexpr auto subspan(Range&& range, size_t offset, size_t count = std::dynamic_extent)
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{
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	return std::span(std::forward<Range>(range)).subspan(offset, count);
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}
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template<size_t Count, std::ranges::range Range>
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[[nodiscard]] constexpr auto subspan(Range&& range, size_t offset = 0)
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{
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	return std::span(std::forward<Range>(range)).subspan(offset).template first<Count>();
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}
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template<typename T, size_t Size>
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[[nodiscard]] inline auto as_byte_span(std::span<T, Size> s)
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{
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	return std::span{std::bit_cast<const uint8_t*>(s.data()), s.size_bytes()};
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}
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#endif