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construct huffman table from symbol spans
Define class template `symbol_span` that represents an inclusive range
from first to last. The `symbol_bitsize` constructor of `huffman::table`
now takes a range of pair-likes of `symbol_span` and bitsize, allowin
gthe same bitsize to be associated with a contiguous range of symbols.
For example, the static Huffman tree corresponding to the literal/length
alphabet in section 3.2.6 of the DEFLATE RFC can be defined as:
constexpr auto table =
huffman::table<std::uint16_t, 288>{
huffman::symbol_bitsize,
{{{ 0, 143}, 8},
{{144, 255}, 9},
{{256, 279}, 7},
{{280, 287}, 8}}};
resolves #91
Change-Id: I50f7ea63561de0bb785c85467cdb943829b65edf
Co-Authored-By: Gary Miguel <[email protected]>- Loading branch information
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,120 @@ | ||
| #pragma once | ||
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| #include <cstddef> | ||
| #include <iterator> | ||
| #include <numeric> | ||
| #include <ranges> | ||
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| namespace starflate::huffman::detail { | ||
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| template <std::ranges::view V> | ||
| class flattened_symbol_bitsize_view | ||
| : public std::ranges::view_interface<flattened_symbol_bitsize_view<V>> | ||
| { | ||
| V base_; | ||
| std::size_t size_; | ||
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| using child_view_type = std::remove_cvref_t<std::ranges::range_value_t<V>>; | ||
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| public: | ||
| using base_type = V; | ||
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| class iterator | ||
| { | ||
| const flattened_symbol_bitsize_view* parent_{}; | ||
| std::size_t offset1_{}; | ||
| std::size_t offset2_{}; | ||
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| public: | ||
| using iterator_category = std::forward_iterator_tag; | ||
| using difference_type = std::ranges::range_difference_t<child_view_type>; | ||
| using value_type = std::ranges::range_value_t<child_view_type>; | ||
| using reference = std::ranges::range_reference_t<child_view_type>; | ||
| using pointer = void; | ||
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| iterator() = default; | ||
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| constexpr iterator( | ||
| const flattened_symbol_bitsize_view& parent, | ||
| std::size_t offset1, | ||
| std::size_t offset2) | ||
| : parent_{&parent}, offset1_{offset1}, offset2_{offset2} | ||
| {} | ||
|
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||
| [[nodiscard]] | ||
| constexpr auto | ||
| operator*() const -> reference | ||
| { | ||
| using D = difference_type; | ||
| return parent_ | ||
| ->base()[static_cast<D>(offset1_)][static_cast<D>(offset2_)]; | ||
| } | ||
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| constexpr auto operator++() & -> iterator& | ||
| { | ||
| using D = difference_type; | ||
|
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| if (++offset2_ == | ||
| static_cast<std::size_t>( | ||
| parent_->base()[static_cast<D>(offset1_)].size())) { | ||
| ++offset1_; | ||
| offset2_ = {}; | ||
| } | ||
|
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| return *this; | ||
| } | ||
|
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| constexpr auto operator++(int) -> iterator | ||
| { | ||
| auto tmp = *this; | ||
| ++*this; | ||
| return tmp; | ||
| } | ||
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| friend constexpr auto | ||
| operator==(const iterator&, const iterator&) -> bool = default; | ||
| }; | ||
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| constexpr explicit flattened_symbol_bitsize_view(V base) | ||
| : base_{std::move(base)}, | ||
| size_{std::accumulate( | ||
| std::ranges::cbegin(base_), | ||
| std::ranges::cend(base_), | ||
| 0UZ, | ||
| [](auto acc, const auto& subrange) { | ||
| return acc + subrange.size(); | ||
| })} | ||
| {} | ||
|
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| [[nodiscard]] | ||
| constexpr auto base() const -> base_type | ||
| { | ||
| return base_; | ||
| } | ||
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| [[nodiscard]] | ||
| constexpr auto size() const -> std::size_t | ||
| { | ||
| return size_; | ||
| } | ||
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| [[nodiscard]] | ||
| constexpr auto begin() const -> iterator | ||
| { | ||
| return {*this, 0, 0}; | ||
| } | ||
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| [[nodiscard]] | ||
| constexpr auto end() const -> iterator | ||
| { | ||
| return {*this, base().size(), 0}; | ||
| } | ||
| }; | ||
|
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| } // namespace starflate::huffman::detail | ||
|
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| // flattened_symbol_bitsize_view is only created to adapt an input range during | ||
| // construction | ||
| template <class V> | ||
| inline constexpr bool std::ranges::enable_borrowed_range< | ||
| ::starflate::huffman::detail::flattened_symbol_bitsize_view<V>> = true; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,27 @@ | ||
| #pragma once | ||
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| #include <type_traits> | ||
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| namespace starflate::huffman::detail { | ||
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| /// Checks if a type is a specialization of a class template | ||
| /// @tparam T type | ||
| /// @tparam primary class template | ||
| /// | ||
| /// @see https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2098r1.pdf | ||
| /// | ||
| /// | ||
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| template <class T, template <class...> class primary> | ||
| struct is_specialization_of : std::false_type | ||
| {}; | ||
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| template <template <class...> class primary, class... Args> | ||
| struct is_specialization_of<primary<Args...>, primary> : std::true_type | ||
| {}; | ||
|
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| template <class T, template <class...> class primary> | ||
| inline constexpr auto is_specialization_of_v = | ||
| is_specialization_of<T, primary>::value; | ||
|
|
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| } // namespace starflate::huffman::detail |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| #pragma once | ||
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| #include "huffman/src/utility.hpp" | ||
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| #include <concepts> | ||
| #include <ranges> | ||
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| namespace starflate::huffman { | ||
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| /// An inclusive span of symbols | ||
| /// | ||
| template <symbol S> | ||
| class symbol_span : public std::ranges::view_interface<symbol_span<S>> | ||
| { | ||
| S first_; | ||
| S last_; | ||
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| using range_type = std::ranges::iota_view<S, S>; | ||
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| constexpr auto as_range() const -> range_type | ||
| { | ||
| auto tmp = last_; | ||
| return range_type{first_, ++tmp}; | ||
| } | ||
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| public: | ||
| using symbol_type = S; | ||
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| using iterator = std::ranges::iterator_t<range_type>; | ||
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| /// Construct a symbol span of a single symbol | ||
| /// @param first symbol | ||
| /// | ||
| constexpr symbol_span(symbol_type first) : symbol_span{first, first} {} | ||
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| /// Construct a symbol span from first to last, inclusive | ||
| /// @param first, last inclusive symbol range | ||
| /// @pre first <= last | ||
| /// | ||
| constexpr symbol_span(symbol_type first, symbol_type last) | ||
| : first_{first}, last_{last} | ||
| { | ||
| assert(first <= last); | ||
| } | ||
|
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| [[nodiscard]] | ||
| constexpr auto begin() const -> iterator | ||
| { | ||
| return as_range().begin(); | ||
| } | ||
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| [[nodiscard]] | ||
| constexpr auto end() const -> iterator | ||
| { | ||
| return as_range().end(); | ||
| } | ||
| }; | ||
|
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| } // namespace starflate::huffman |
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