Add constexpr endianness utilities

Author: bdero

fml/BUILD.gn

@@ -268,6 +268,7 @@ if (enable_unittests) {
       "backtrace_unittests.cc",
       "base32_unittest.cc",
       "command_line_unittest.cc",
+      "endianness_unittests.cc",
       "file_unittest.cc",
       "hash_combine_unittests.cc",
       "hex_codec_unittest.cc",

fml/endianness.h

@@ -0,0 +1,70 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_FML_ENDIANNESS_H_
+#define FLUTTER_FML_ENDIANNESS_H_
+
+#include <cstdint>
+#include <type_traits>
+#if defined(_MSC_VER)
+#include "intrin.h"
+#endif
+
+#include "flutter/fml/build_config.h"
+
+// Compiler intrinsics for flipping endianness.
+#define BYTESWAP16(n) __builtin_bswap16(n)
+#define BYTESWAP32(n) __builtin_bswap32(n)
+#define BYTESWAP64(n) __builtin_bswap64(n)
+
+#if defined(_MSC_VER)
+#define BYTESWAP16(n) _byteswap_ushort(n)
+#define BYTESWAP32(n) _byteswap_ulong(n)
+#define BYTESWAP64(n) _byteswap_uint64(n)
+#endif
+
+namespace fml {
+
+/// @brief  Flips the endianness of the given value.
+template <typename T>
+constexpr T ByteSwap(T n) {
+  if constexpr (sizeof(T) == 1) {
+    return n;
+  } else if constexpr (sizeof(T) == 2) {
+    return (T)BYTESWAP16((uint16_t)n);
+  } else if constexpr (sizeof(T) == 4) {
+    return (T)BYTESWAP32((uint32_t)n);
+  } else if constexpr (sizeof(T) == 8) {
+    return (T)BYTESWAP64((uint64_t)n);
+  } else {
+    static_assert(!sizeof(T), "Unsupported size");
+  }
+}
+
+/// @brief  Convert a known big endian value to match the endianness of the
+///         current architecture. This is effectively a cross platform
+///         ntohl/ntohs (as network byte order is always Big Endian).
+template <typename T>
+constexpr T BigEndianToArch(T n) {
+#if ARCH_CPU_LITTLE_ENDIAN
+  return ByteSwap<T>(n);
+#else
+  return n;
+#endif
+}
+
+/// @brief  Convert a known little endian value to match the endianness of the
+///         current architecture.
+template <typename T>
+constexpr T LittleEndianToArch(T n) {
+#if !ARCH_CPU_LITTLE_ENDIAN
+  return ByteSwap<T>(n);
+#else
+  return n;
+#endif
+}
+
+}  // namespace fml
+
+#endif  // FLUTTER_FML_ENDIANNESS_H_

fml/endianness_unittests.cc

@@ -0,0 +1,37 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/endianness.h"
+
+#include "flutter/testing/testing.h"
+
+namespace fml {
+namespace testing {
+
+TEST(EndiannessTest, ByteSwap) {
+  ASSERT_EQ(ByteSwap<int16_t>(0x1122), 0x2211);
+  ASSERT_EQ(ByteSwap<int32_t>(0x11223344), 0x44332211);
+  ASSERT_EQ(ByteSwap<uint64_t>(0x1122334455667788), 0x8877665544332211);
+}
+
+TEST(EndiannessTest, BigEndianToArch) {
+#if ARCH_CPU_LITTLE_ENDIAN
+  uint32_t expected = 0x44332211;
+#else
+  uint32_t expected = 0x11223344;
+#endif
+  ASSERT_EQ(BigEndianToArch(0x11223344u), expected);
+}
+
+TEST(EndiannessTest, LittleEndianToArch) {
+#if ARCH_CPU_LITTLE_ENDIAN
+  uint32_t expected = 0x11223344;
+#else
+  uint32_t expected = 0x44332211;
+#endif
+  ASSERT_EQ(LittleEndianToArch(0x11223344u), expected);
+}
+
+}  // namespace testing
+}  // namespace fml