test: Add example bit_cast tests

test/unittests/CMakeLists.txt

@@ -10,6 +10,7 @@ target_link_libraries(fizzy-unittests PRIVATE fizzy::fizzy fizzy::test-utils GTe
 target_sources(
     fizzy-unittests PRIVATE
     api_test.cpp
+    bit_cast_test.cpp
     constexpr_vector_test.cpp
     end_to_end_test.cpp
     execute_call_test.cpp

test/unittests/bit_cast_test.cpp

@@ -0,0 +1,46 @@
+// Fizzy: A fast WebAssembly interpreter
+// Copyright 2020 The Fizzy Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "cxx20/bit.hpp"
+#include <gtest/gtest.h>
+#include <array>
+
+using namespace fizzy;
+using namespace testing;
+
+
+TEST(bit_cast, double_to_uint64)
+{
+    // A test case from https://en.cppreference.com/w/cpp/numeric/bit_cast#Example.
+    EXPECT_EQ(bit_cast<uint64_t>(19880124.0), 0x4172f58bc0000000);
+}
+
+TEST(bit_cast, uint64_to_double)
+{
+    // A test case from https://en.cppreference.com/w/cpp/numeric/bit_cast#Example.
+    EXPECT_EQ(bit_cast<double>(uint64_t{0x3fe9000000000000}), 0.781250);
+}
+
+TEST(bit_cast, uint32_to_int32)
+{
+    EXPECT_EQ(bit_cast<int32_t>(uint32_t{0x80000000}), -2147483648);
+    EXPECT_EQ(bit_cast<int32_t>(uint32_t{0xffffffff}), -1);
+}
+
+TEST(bit_cast, int32_to_uint32)
+{
+    EXPECT_EQ(bit_cast<uint32_t>(int32_t{-2}), 0xfffffffe);
+    EXPECT_EQ(bit_cast<uint32_t>(int32_t{1}), 1);
+}
+
+TEST(bit_cast, uint32_to_array)
+{
+    // Uses "byte-symmetric" value to avoid handling endianness.
+    std::array<uint8_t, 4> bytes;
+    bytes = bit_cast<decltype(bytes)>(uint32_t{0xaabbbbaa});
+    EXPECT_EQ(bytes[0], 0xaa);
+    EXPECT_EQ(bytes[1], 0xbb);
+    EXPECT_EQ(bytes[2], 0xbb);
+    EXPECT_EQ(bytes[3], 0xaa);
+}