refactor: <algorithm.h> header added

Should be replaced with `<algorithm>` when C++20 modules will be used. Right now this header is too expensive to compile.

src/core/include/units/bits/external/algorithm.h

@@ -0,0 +1,76 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <units/bits/external/hacks.h>  // IWYU pragma: keep
+#include <compare>
+
+namespace units::detail {
+
+template<class InputIt1, class InputIt2>
+constexpr bool equal(InputIt1 first1, InputIt1 last1, InputIt2 first2)
+{
+  for (; first1 != last1; ++first1, ++first2) {
+    if (!(*first1 == *first2)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+template<class InputIt, class UnaryPredicate>
+constexpr InputIt find_if(InputIt first, InputIt last, UnaryPredicate p)
+{
+  for (; first != last; ++first) {
+    if (p(*first)) {
+      return first;
+    }
+  }
+  return last;
+}
+
+template<class I1, class I2, class Cmp>
+constexpr auto lexicographical_compare_three_way(I1 f1, I1 l1, I2 f2, I2 l2, Cmp comp) -> decltype(comp(*f1, *f2))
+{
+  using ret_t = decltype(comp(*f1, *f2));
+  static_assert(std::disjunction_v<std::is_same<ret_t, std::strong_ordering>, std::is_same<ret_t, std::weak_ordering>,
+                                   std::is_same<ret_t, std::partial_ordering>>,
+                "The return type must be a comparison category type.");
+
+  bool exhaust1 = (f1 == l1);
+  bool exhaust2 = (f2 == l2);
+  for (; !exhaust1 && !exhaust2; exhaust1 = (++f1 == l1), exhaust2 = (++f2 == l2))
+    if (auto c = comp(*f1, *f2); c != 0) return c;
+
+  return !exhaust1   ? std::strong_ordering::greater
+         : !exhaust2 ? std::strong_ordering::less
+                     : std::strong_ordering::equal;
+}
+
+template<class I1, class I2>
+constexpr auto lexicographical_compare_three_way(I1 f1, I1 l1, I2 f2, I2 l2)
+{
+  return ::units::detail::lexicographical_compare_three_way(f1, l1, f2, l2, std::compare_three_way());
+}
+
+}  // namespace units::detail

src/core/include/units/bits/external/fixed_string.h

@@ -23,6 +23,8 @@
 #pragma once
 
 #include <units/bits/external/hacks.h>  // IWYU pragma: keep
+// TODO use <algorithm> when moved to C++20 modules (parsing takes too long for each translation unit)
+#include <units/bits/external/algorithm.h>
 
 // IWYU pragma: begin_exports
 #include <compare>
@@ -31,7 +33,6 @@
 
 #include <cstddef>
 
-// TODO use <algorithm> when moved to C++20 modules (parsing takes too long for each translation unit)
 
 namespace units {
 
@@ -83,11 +84,7 @@ struct basic_fixed_string {
   [[nodiscard]] constexpr bool operator==(const basic_fixed_string& other) const
   {
     if (size() != other.size()) return false;
-    for (size_t i = 0; i != size(); ++i) {
-      if ((*this)[i] != other[i]) return false;
-    }
-    return true;
-    // return std::ranges::equal(*this, other);
+    return detail::equal(begin(), end(), other.begin());  // TODO std::ranges::equal(*this, other)
   }
 
   template<std::size_t N2>
@@ -100,19 +97,8 @@ struct basic_fixed_string {
   [[nodiscard]] friend constexpr auto operator<=>(const basic_fixed_string& lhs,
                                                   const basic_fixed_string<CharT, N2>& rhs)
   {
-    auto first1 = lhs.begin();
-    const auto last1 = lhs.end();
-    auto first2 = rhs.begin();
-    const auto last2 = rhs.end();
-    auto comp = std::compare_three_way();
-
-    for (; first1 != last1 && first2 != last2; ++first1, ++first2)
-      if (auto cmp = comp(*first1, *first2); cmp != 0) return cmp;
-
-    return first1 != last1   ? std::strong_ordering::greater
-           : first2 != last2 ? std::strong_ordering::less
-                             : std::strong_ordering::equal;
-    // return std::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
+    // TODO std::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
+    return detail::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
   }
 };