Added preview::endian

cmake/RunConfiguration.cmake

@@ -2,6 +2,7 @@ include(CheckCXXSourceCompiles)
 include(CheckCXXCompilerFlag)
 include(CheckCXXSymbolExists)
 
+include(config/CheckEndianness)
 include(config/HaveBuiltinBitCast)
 include(config/HaveBuiltinConstexprAddressof)
 include(config/HaveContiguousIteratorTag)

cmake/config/CheckEndianness.cmake

@@ -0,0 +1,62 @@
+set(AllTypes1Byte_Source
+"int main() {
+    static_asset(sizeof(char) == 1) &&
+    static_asset(sizeof(short) == 1) &&
+    static_asset(sizeof(int) == 1) &&
+    static_asset(sizeof(long) == 1) &&
+    static_asset(sizeof(long long) == 1) &&
+    static_asset(sizeof(bool) == 1);
+}")
+
+check_cxx_source_compiles(AllTypes1Byte_Source PREVIEW_ARE_ALL_TYPES_1_BYTE)
+
+set(PREVIEW_BIG_ENDIAN 0)
+set(PREVIEW_LITTLE_ENDIAN 1)
+set(PREVIEW_OTHER_ENDIAN 2)
+
+file(WRITE ${CMAKE_BINARY_DIR}/CheckEndian.cpp
+"#include <cstdint>
+#include <fstream>
+
+int main(int argc, char* argv[]) {
+    const std::uint32_t val{ 0x01'23'45'67 };
+    const std::uint8_t* ptr{ reinterpret_cast<const std::uint8_t*>(&val) };
+    std::ofstream out{ argv[1] };
+
+    if (ptr[0] == 0x01 && ptr[1] == 0x23 && ptr[2] == 0x45 && ptr[3] == 0x67) {
+        out << ${PREVIEW_BIG_ENDIAN} << std::endl;
+    } else if (ptr[0] == 0x67 && ptr[1] == 0x45 && ptr[2] == 0x23 && ptr[3] == 0x01) {
+        out << ${PREVIEW_LITTLE_ENDIAN} << std::endl;
+    } else {
+        out << ${PREVIEW_OTHER_ENDIAN} << std::endl;
+    }
+}")
+
+if (PREVIEW_ARE_ALL_TYPES_1_BYTE EQUAL 1)
+    add_compile_definitions(PREVIEW_BIG_ENDIAN=0)
+    add_compile_definitions(PREVIEW_LITTLE_ENDIAN=0)
+    add_compile_definitions(PREVIEW_OTHER_ENDIAN=0)
+else()
+    add_compile_definitions(PREVIEW_BIG_ENDIAN=${PREVIEW_BIG_ENDIAN})
+    add_compile_definitions(PREVIEW_LITTLE_ENDIAN=${PREVIEW_LITTLE_ENDIAN})
+    add_compile_definitions(PREVIEW_OTHER_ENDIAN=${PREVIEW_OTHER_ENDIAN})
+endif()
+
+try_run(
+    runres compileres ${CMAKE_BINARY_DIR}
+    SOURCES ${CMAKE_BINARY_DIR}/CheckEndian.cpp
+    ARGS ${CMAKE_BINARY_DIR}/endian.txt
+)
+
+file(READ ${CMAKE_BINARY_DIR}/endian.txt PREVIEW_ENDIAN)
+
+if(PREVIEW_ENDIAN EQUAL ${PREVIEW_BIG_ENDIAN})
+    message(STATUS "Big endian")
+    add_compile_definitions(PREVIEW_ENDIAN=${PREVIEW_BIG_ENDIAN})
+elseif(PREVIEW_ENDIAN EQUAL ${PREVIEW_LITTLE_ENDIAN})
+    message(STATUS "Little endian")
+    add_compile_definitions(PREVIEW_ENDIAN=${PREVIEW_LITTLE_ENDIAN})
+else()
+    message(STATUS "Other endian")
+    add_compile_definitions(PREVIEW_ENDIAN=${PREVIEW_OTHER_ENDIAN})
+endif()

include/preview/__bit/endian.h

@@ -0,0 +1,26 @@
+//
+// Created by Chi-Iroh on 09/11/2024.
+//
+
+#ifndef PREVIEW_BIT_ENDIAN_H_
+#define PREVIEW_BIT_ENDIAN_H_
+
+#include "preview/config.h"
+
+#if PREVIEW_CXX_VERSION >= 20
+  #include <bit>
+
+  namespace preview {
+      using endian = std::endian;
+  }
+#else
+  namespace preview {
+    enum class endian {
+      little = PREVIEW_LITTLE_ENDIAN,
+      big = PREVIEW_BIG_ENDIAN,
+      native = PREVIEW_ENDIAN
+    };
+  };
+#endif
+
+#endif

include/preview/bit.h

@@ -7,5 +7,6 @@
 
 #include "preview/__bit/bit_cast.h"
 #include "preview/__bit/byteswap.h"
+#include "preview/__bit/endian.h"
 
 #endif // PREVIEW_BIT_H_

test/bit.cc

@@ -60,3 +60,26 @@ TEST(VERSIONED(bit), byteswap_signed) {
   constexpr std::int64_t qword_same{ 0x44'44'44'44'44'44'44'44 };
   EXPECT_EQ(preview::byteswap<std::int64_t>(qword_same), qword_same);
 }
+
+#if PREVIEW_CXX >= 17
+  #define IF_CONSTEXPR if constexpr
+#else
+  #define IF_CONSTEXPR if
+#endif
+
+TEST(VERSIONED(bit), little_endian) {
+  const std::uint32_t n{ 0x01'23'45'67 };
+  const std::uint8_t* const ptr{ reinterpret_cast<const std::uint8_t*>(&n) };
+
+  IF_CONSTEXPR (preview::endian::native == preview::endian::little) {
+    EXPECT_EQ(ptr[0], 0x67);
+    EXPECT_EQ(ptr[1], 0x45);
+    EXPECT_EQ(ptr[2], 0x23);
+    EXPECT_EQ(ptr[3], 0x01);
+  } else IF_CONSTEXPR (preview::endian::native == preview::endian::big) {
+    EXPECT_EQ(ptr[0], 0x01);
+    EXPECT_EQ(ptr[1], 0x23);
+    EXPECT_EQ(ptr[2], 0x45);
+    EXPECT_EQ(ptr[3], 0x67);
+  }
+}