add huffman table constructor from symbol-bitsize range

Add a constructor to huffman::table that takes a range of symbol-bitsize
tuples.

This commit also moves public tag types into a utility header.

Change-Id: Ia125173ce91e2e189c23de0956d9eaa7aa51762c

huffman/BUILD.bazel

@@ -14,6 +14,7 @@ cc_library(
         "src/detail/table_storage.hpp",
         "src/encoding.hpp",
         "src/table.hpp",
+        "src/utility.hpp",
     ],
     hdrs = ["huffman.hpp"],
     visibility = ["//:__subpackages__"],

huffman/src/detail/table_storage.hpp

@@ -3,6 +3,7 @@
 #include "huffman/src/code.hpp"
 #include "huffman/src/detail/static_vector.hpp"
 #include "huffman/src/encoding.hpp"
+#include "huffman/src/utility.hpp"
 
 #include <algorithm>
 #include <cassert>
@@ -13,18 +14,7 @@
 #include <type_traits>
 #include <vector>
 
-namespace starflate::huffman {
-
-/// Disambiguation tag to specify a table is constructed with a code-symbol
-///    mapping
-///
-struct table_contents_tag
-{
-  explicit table_contents_tag() = default;
-};
-inline constexpr auto table_contents = table_contents_tag{};
-
-namespace detail {
+namespace starflate::huffman::detail {
 
 struct frequency_tag
 {
@@ -55,7 +45,6 @@ class table_storage : table_storage_base_t<IntrusiveNode, Extent>
   template <class R>
   constexpr table_storage(
       frequency_tag, const R& frequencies, std::optional<symbol_type> eot)
-      : base_type{}
   {
     base_type::reserve(
         std::ranges::size(frequencies) + std::size_t{eot.has_value()});
@@ -74,7 +63,6 @@ class table_storage : table_storage_base_t<IntrusiveNode, Extent>
   template <class R>
   constexpr table_storage(
       data_tag, const R& data, std::optional<symbol_type> eot)
-      : base_type{}
   {
     if (eot) {
       base_type::emplace_back(*eot, 1UZ);
@@ -97,7 +85,7 @@ class table_storage : table_storage_base_t<IntrusiveNode, Extent>
   }
 
   template <class R>
-  constexpr table_storage(table_contents_tag, const R& map) : base_type{}
+  constexpr table_storage(table_contents_tag, const R& map)
   {
     const auto as_code = [](auto& node) -> auto& {
       return static_cast<code&>(node);
@@ -116,9 +104,6 @@ class table_storage : table_storage_base_t<IntrusiveNode, Extent>
       as_symbol(*it) = s;
       ++it;
     }
-
-    assert(std::ranges::unique(*this, {}, as_code).empty());
-    assert(std::ranges::unique(*this, {}, as_symbol).empty());
   }
 
   using base_type::begin;
@@ -131,5 +116,4 @@ class table_storage : table_storage_base_t<IntrusiveNode, Extent>
   using base_type::size;
 };
 
-}  // namespace detail
-}  // namespace starflate::huffman
+}  // namespace starflate::huffman::detail

huffman/src/table.hpp

@@ -3,6 +3,7 @@
 #include "huffman/src/detail/element_base_iterator.hpp"
 #include "huffman/src/detail/table_node.hpp"
 #include "huffman/src/detail/table_storage.hpp"
+#include "huffman/src/utility.hpp"
 
 #include <algorithm>
 #include <compare>
@@ -22,8 +23,47 @@
 
 namespace starflate::huffman {
 
-template <class T, std::size_t N>
-using c_array = T[N];
+namespace detail {
+
+/// Convert an unsigned integer to signed
+///
+template <std::signed_integral S, std::unsigned_integral U>
+static constexpr auto to_signed(U uint)
+{
+  using C [[maybe_unused]] = std::common_type_t<std::make_unsigned_t<S>, U>;
+
+  assert(static_cast<C>(uint) < static_cast<C>(std::numeric_limits<S>::max()));
+  return static_cast<S>(uint);
+}
+
+/// Finds the next internal node that satifies a predicate
+///
+template <std::random_access_iterator I, std::indirect_unary_predicate<I> P>
+constexpr static auto find_node_if(I first, I last, P pred)
+{
+  using S = std::iter_difference_t<I>;
+
+  for (; first != last; first += to_signed<S>(first->node_size())) {
+    if (pred(*first)) {
+      break;
+    }
+  }
+
+  return first;
+}
+
+/// Transforms a symbol-bitsize range to a code-symbol range
+///
+template <class R>
+constexpr auto to_code_symbol(const R& rng)
+{
+  return std::views::transform(rng, [](const auto& elem) {
+    const auto& [symbol, bitsize] = elem;
+    return std::tuple{code{bitsize, {}}, symbol};
+  });
+}
+
+}  // namespace detail
 
 /// Huffman code table
 /// @tparam Symbol symbol type
@@ -44,31 +84,10 @@ class table
 
   detail::table_storage<node_type, Extent> table_;
 
-  template <std::unsigned_integral U>
-  static constexpr auto to_index(U uint)
+  constexpr auto encode_symbols() -> void
   {
     using S = std::ranges::range_difference_t<decltype(table_)>;
-    using C [[maybe_unused]] = std::common_type_t<std::make_unsigned_t<S>, U>;
-
-    assert(
-        static_cast<C>(uint) < static_cast<C>(std::numeric_limits<S>::max()));
-    return static_cast<S>(uint);
-  }
 
-  template <std::forward_iterator I, std::indirect_unary_predicate<I> P>
-  constexpr static auto find_node_if(I first, I last, P pred)
-  {
-    for (; first != last; first += to_index(first->node_size())) {
-      if (pred(*first)) {
-        break;
-      }
-    }
-
-    return first;
-  }
-
-  constexpr auto encode_symbols() -> void
-  {
     auto reversed = std::views::reverse(table_);
 
     // precondition, audit
@@ -79,13 +98,13 @@ class table
     const auto last = reversed.end();
 
     while (first->node_size() != total_size) {
-      join_reversed(first[0], first[to_index(first->node_size())]);
+      join_reversed(first[0], first[detail::to_signed<S>(first->node_size())]);
 
       const auto has_higher_freq = [&first](const auto& n) {
         return n.frequency() > first->frequency();
       };
 
-      auto lower = first + to_index(first->node_size());
+      auto lower = first + detail::to_signed<S>(first->node_size());
       auto upper = find_node_if(lower, last, has_higher_freq);
 
       // re-sort after creating a new internal node
@@ -149,13 +168,13 @@ class table
   }
 
 public:
-  /// Code point type
+  /// Symbol type
   ///
-  using encoding_type = encoding<Symbol>;
+  using symbol_type = Symbol;
 
-  /// Symbol type
+  /// Code point type
   ///
-  using symbol_type = typename encoding_type::symbol_type;
+  using encoding_type = encoding<symbol_type>;
 
   /// Const iterator type
   ///
@@ -176,13 +195,6 @@ class table
   ///
   /// @{
 
-  template <std::ranges::sized_range R>
-    requires std::convertible_to<
-        std::ranges::range_value_t<R>,
-        std::tuple<symbol_type, std::size_t>>
-  constexpr explicit table(const R& frequencies) : table{frequencies, {}}
-  {}
-
   template <std::ranges::sized_range R>
     requires std::convertible_to<
         std::ranges::range_value_t<R>,
@@ -194,6 +206,13 @@ class table
     set_skip_fields();
   }
 
+  template <std::ranges::sized_range R>
+    requires std::convertible_to<
+        std::ranges::range_value_t<R>,
+        std::tuple<symbol_type, std::size_t>>
+  constexpr explicit table(const R& frequencies) : table{frequencies, {}}
+  {}
+
   template <std::integral I, auto N>
   constexpr explicit table(
       const c_array<std::pair<symbol_type, I>, N>& frequencies)
@@ -251,21 +270,51 @@ class table
             std::tuple_element_t<1, std::ranges::range_value_t<R>>,
             symbol_type>)
   constexpr table(table_contents_tag, const R& map)
-      : table_{table_contents_tag{}, map}
+      : table_{table_contents, map}
   {
     set_skip_fields();
   }
 
   template <std::size_t N>
   constexpr table(
       table_contents_tag, const c_array<std::pair<code, symbol_type>, N>& map)
-      : table_{table_contents_tag{}, map}
+      : table_{table_contents, map}
   {
     set_skip_fields();
   }
 
   /// @}
 
+  /// Constructs a `table` from a symbol-bitsize mapping
+  /// @tparam R sized-range of symbol-bitsize tuple-likes
+  /// @param rng range of symbol-bitsize tuple-likes
+  /// @pre all symbols are unique
+  /// @pre the number of symbols with the same bitsize does not exceed the
+  ///     available number of prefix free codes with that bitsize
+  ///
+  /// @{
+
+  template <std::ranges::sized_range R>
+    requires std::convertible_to<
+        std::ranges::range_reference_t<R>,
+        std::tuple<symbol_type, std::uint8_t>>
+  constexpr table(symbol_bitsize_tag, const R& map)
+      : table{table_contents, detail::to_code_symbol(map)}
+  {
+    canonicalize();
+  }
+
+  template <std::size_t N>
+  constexpr table(
+      symbol_bitsize_tag,
+      const c_array<std::pair<symbol_type, std::uint8_t>, N>& map)
+      : table{table_contents, detail::to_code_symbol(map)}
+  {
+    canonicalize();
+  }
+
+  /// @}
+
   /// Returns an iterator to the first `encoding`
   ///
   /// @note elements are ordered by code bitsize. If multiple elements have the
@@ -461,4 +510,12 @@ template <class R>
 table(table_contents_tag, const R&)
     -> table<detail::tuple_arg_t<1, R>, detail::tuple_size_v<R>()>;
 
+template <class S, class I, std::size_t N>
+table(symbol_bitsize_tag, const c_array<std::pair<S, I>, N>&) -> table<S, N>;
+
+template <class R>
+  requires (detail::tuple_size_v<std::ranges::range_value_t<R>>() == 2)
+table(symbol_bitsize_tag, const R&)
+    -> table<detail::tuple_arg_t<0, R>, detail::tuple_size_v<R>()>;
+
 }  // namespace starflate::huffman

huffman/src/utility.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstddef>
+
+namespace starflate::huffman {
+
+/// Convenience alias for a C-style array
+///
+template <class T, std::size_t N>
+using c_array = T[N];
+
+/// Disambiguation tag to specify a table is constructed with a code-symbol
+///    mapping
+///
+struct table_contents_tag
+{
+  explicit table_contents_tag() = default;
+};
+inline constexpr auto table_contents = table_contents_tag{};
+
+/// Disambiguation tag to specify a table is constructed with a symbol-bitsize
+///    mapping
+///
+struct symbol_bitsize_tag
+{
+  explicit symbol_bitsize_tag() = default;
+};
+inline constexpr auto symbol_bitsize = symbol_bitsize_tag{};
+
+}  // namespace starflate::huffman

huffman/test/BUILD.bazel

@@ -21,19 +21,29 @@ cc_test(
 )
 
 cc_test(
-    name = "table_from_frequencies_test",
+    name = "table_canonicalize_test",
     timeout = "short",
-    srcs = ["table_from_frequencies_test.cpp"],
+    srcs = ["table_canonicalize_test.cpp"],
     deps = [
         "//huffman",
         "@boost_ut",
     ],
 )
 
 cc_test(
-    name = "table_canonicalize_test",
+    name = "table_find_code_test",
     timeout = "short",
-    srcs = ["table_canonicalize_test.cpp"],
+    srcs = ["table_find_code_test.cpp"],
+    deps = [
+        "//huffman",
+        "@boost_ut",
+    ],
+)
+
+cc_test(
+    name = "table_from_frequencies_test",
+    timeout = "short",
+    srcs = ["table_from_frequencies_test.cpp"],
     deps = [
         "//huffman",
         "@boost_ut",
@@ -61,9 +71,9 @@ cc_test(
 )
 
 cc_test(
-    name = "table_find_code_test",
+    name = "table_from_symbol_bitsize_test",
     timeout = "short",
-    srcs = ["table_find_code_test.cpp"],
+    srcs = ["table_from_symbol_bitsize_test.cpp"],
     deps = [
         "//huffman",
         "@boost_ut",