From 101ac1cd5045d2b153a3fc865909953f40a16d27 Mon Sep 17 00:00:00 2001
From: Marcus Holland-Moritz <github@mhxnet.de>
Date: Sun, 27 Jul 2025 15:02:25 +0200
Subject: [PATCH] wip: support big endian

---
 include/dwarfs/endian.h  | 106 +++++++++++++++++++++++++++++++++++++++
 include/dwarfs/fstypes.h |   9 ++--
 2 files changed, 111 insertions(+), 4 deletions(-)
 create mode 100644 include/dwarfs/endian.h

diff --git a/include/dwarfs/endian.h b/include/dwarfs/endian.h
new file mode 100644
index 00000000..e213280e
--- /dev/null
+++ b/include/dwarfs/endian.h
@@ -0,0 +1,106 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * 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.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <bit>
+#include <compare>
+#include <concepts>
+#include <cstdint>
+#include <type_traits>
+
+namespace dwarfs {
+
+template <std::unsigned_integral T, std::endian Endian>
+class boxed_endian {
+ public:
+  static_assert(Endian == std::endian::little || Endian == std::endian::big);
+
+  constexpr boxed_endian() = default;
+  constexpr explicit boxed_endian(T v) noexcept
+      : raw_{swap(v)} {}
+
+  constexpr operator T() const noexcept { return swap(raw_); }
+
+  template <typename E>
+    requires std::is_enum_v<E>
+  constexpr explicit operator E() const noexcept {
+    return static_cast<E>(swap(raw_));
+  }
+
+  constexpr T load() const noexcept { return swap(raw_); }
+
+  constexpr boxed_endian& operator=(T v) noexcept {
+    raw_ = swap(v);
+    return *this;
+  }
+
+  friend constexpr auto
+  operator<=>(boxed_endian lhs, boxed_endian rhs) noexcept {
+    return static_cast<T>(lhs) <=> static_cast<T>(rhs);
+  }
+
+  friend constexpr bool
+  operator==(boxed_endian lhs, boxed_endian rhs) noexcept {
+    return static_cast<T>(lhs) == static_cast<T>(rhs);
+  }
+
+ private:
+  T raw_{};
+
+  static constexpr T swap(T value) noexcept {
+    if constexpr (std::endian::native == Endian) {
+      return value;
+    } else if constexpr (sizeof(T) == 1) {
+      return value;
+    } else {
+#if defined(__GNUC__) || defined(__clang__)
+      static_assert(sizeof(T) == 2 || sizeof(T) == 4 || sizeof(T) == 8);
+      if constexpr (sizeof(T) == 2) {
+        return __builtin_bswap16(value);
+      } else if constexpr (sizeof(T) == 4) {
+        return __builtin_bswap32(value);
+      } else if constexpr (sizeof(T) == 8) {
+        return __builtin_bswap64(value);
+      }
+#else
+#error "Unsupported compiler for byte swapping"
+#endif
+    }
+  }
+};
+
+using uint16le_t = boxed_endian<uint16_t, std::endian::little>;
+using uint32le_t = boxed_endian<uint32_t, std::endian::little>;
+using uint64le_t = boxed_endian<uint64_t, std::endian::little>;
+
+static_assert(sizeof(uint16le_t) == 2);
+static_assert(sizeof(uint32le_t) == 4);
+static_assert(sizeof(uint64le_t) == 8);
+
+} // namespace dwarfs
diff --git a/include/dwarfs/fstypes.h b/include/dwarfs/fstypes.h
index 31bb593e..6b501851 100644
--- a/include/dwarfs/fstypes.h
+++ b/include/dwarfs/fstypes.h
@@ -39,6 +39,7 @@
 
 #include <dwarfs/block_compressor.h> // TODO: or the other way round?
 #include <dwarfs/checksum.h>
+#include <dwarfs/endian.h>
 
 namespace dwarfs {
 
@@ -87,10 +88,10 @@ struct section_header_v2 {
   std::array<uint8_t, 32>    //  [8] SHA2-512/256 starting from next field
       sha2_512_256;          //
   uint64_t xxh3_64;          // [40] XXH3-64 starting from next field
-  uint32_t number;           // [48] section number
-  uint16_t type;             // [52] section type
-  uint16_t compression;      // [54] compression
-  uint64_t length;           // [56] length of section
+  uint32le_t number;         // [48] section number
+  uint16le_t type;           // [52] section type
+  uint16le_t compression;    // [54] compression
+  uint64le_t length;         // [56] length of section
 
   std::string to_string() const;
   void dump(std::ostream& os) const;