Restore byteswap utility

modules/core/inc/tactile/core/platform/bits.hpp

@@ -2,9 +2,14 @@
 
 #pragma once
 
-#include <bit>       // endian
-#include <concepts>  // integral, invocable
+#include <algorithm>    // reverse
+#include <bit>          // bit_cast, endian, byteswap
+#include <concepts>     // integral, invocable
+#include <cstddef>      // byte
+#include <type_traits>  // has_unique_object_representations_v
+#include <version>      // __cpp_lib_byteswap
 
+#include "tactile/core/container/array.hpp"
 #include "tactile/core/prelude.hpp"
 
 namespace tactile {
@@ -24,6 +29,30 @@ void each_byte(const IntType value, const CallableType& callable)
   }
 }
 
+/**
+ * \brief Reverses the bytes in an integer value.
+ *
+ * \tparam IntType an integral type.
+ *
+ * \param value an integer value.
+ *
+ * \return a byteswapped integer.
+ */
+template <std::integral IntType>
+[[nodiscard]] constexpr auto reverse_bytes(const IntType value) noexcept -> IntType
+{
+#if __cpp_lib_byteswap >= 202110L
+  return std::byteswap(value);
+#else
+  using ByteArray = Array<std::byte, sizeof(IntType)>;
+
+  const auto bytes = std::bit_cast<ByteArray>(value);
+  std::ranges::reverse(bytes);
+
+  return std::bit_cast<IntType>(bytes);
+#endif
+}
+
 /**
  * \brief Converts a native integer to a little endian integer.
  *
@@ -34,7 +63,7 @@ void each_byte(const IntType value, const CallableType& callable)
 template <std::integral IntType>
 [[nodiscard]] constexpr auto to_little_endian(const IntType value) noexcept -> IntType
 {
-  return (std::endian::native == std::endian::little) ? value : std::byteswap(value);
+  return (std::endian::native == std::endian::little) ? value : reverse_bytes(value);
 }
 
 }  // namespace tactile

modules/core/src/tactile/core/io/tile_matrix_encoding.cpp

@@ -2,7 +2,7 @@
 
 #include "tactile/core/io/tile_matrix_encoding.hpp"
 
-#include <bit>       // endian, byteswap
+#include <bit>       // endian
 #include <concepts>  // same_as
 #include <cstring>   // memcpy
 
@@ -55,7 +55,7 @@ auto tile_matrix_from_byte_stream(const ByteStream& byte_stream,
 
     // Correct the byte ordering if we're on a big endian system.
     if constexpr (std::endian::native == std::endian::big) {
-      tile_id = std::byteswap(tile_id);
+      tile_id = reverse_bytes(tile_id);
     }
 
     // Clear any flipping bits used by Tiled.

modules/core/test/platform/bits_test.cpp

@@ -0,0 +1,27 @@
+// Copyright (C) 2023 Albin Johansson (GNU General Public License v3.0)
+
+#include "tactile/core/platform/bits.hpp"
+
+#include <bit>  // bit_cast
+
+#include <gtest/gtest.h>
+
+#include "tactile/core/container/array.hpp"
+
+using namespace tactile;
+
+TEST(BitUtilities, ReverseBytes)
+{
+  using ByteArray = Array<uint8, sizeof(uint32)>;
+
+  const uint32 original = 0xDEADBEEF;
+  const auto swapped = reverse_bytes(original);
+
+  const auto original_bytes = std::bit_cast<ByteArray>(original);
+  const auto swapped_bytes = std::bit_cast<ByteArray>(swapped);
+
+  EXPECT_EQ(original_bytes.at(0), swapped_bytes.at(3));
+  EXPECT_EQ(original_bytes.at(1), swapped_bytes.at(2));
+  EXPECT_EQ(original_bytes.at(2), swapped_bytes.at(1));
+  EXPECT_EQ(original_bytes.at(3), swapped_bytes.at(0));
+}