3 files changed, 100 insertions, 3 deletions

diff --git a/src/common/bit_field.h b/src/common/bit_field.h
index 21e07925d..bd9e21e1e 100644
--- a/src/common/bit_field.h
+++ b/src/common/bit_field.h
@@ -34,6 +34,7 @@
 #include <limits>
 #include <type_traits>
 #include "common/common_funcs.h"
+#include "common/swap.h"
 
 /*
  * Abstract bitfield class
@@ -108,7 +109,7 @@
  * symptoms.
  */
 #pragma pack(1)
-template <std::size_t Position, std::size_t Bits, typename T>
+template <std::size_t Position, std::size_t Bits, typename T, typename EndianTag = LETag>
 struct BitField {
 private:
     // We hide the copy assigment operator here, because the default copy
@@ -127,6 +128,8 @@ private:
     // We store the value as the unsigned type to avoid undefined behaviour on value shifting
     using StorageType = std::make_unsigned_t<UnderlyingType>;
 
+    using StorageTypeWithEndian = typename AddEndian<StorageType, EndianTag>::type;
+
 public:
     /// Constants to allow limited introspection of fields if needed
     static constexpr std::size_t position = Position;
@@ -172,7 +175,7 @@ public:
     }
 
     constexpr FORCE_INLINE void Assign(const T& value) {
-        storage = (storage & ~mask) | FormatValue(value);
+        storage = (static_cast<StorageType>(storage) & ~mask) | FormatValue(value);
     }
 
     constexpr T Value() const {
@@ -184,7 +187,7 @@ public:
     }
 
 private:
-    StorageType storage;
+    StorageTypeWithEndian storage;
 
     static_assert(bits + position <= 8 * sizeof(T), "Bitfield out of range");
 
@@ -195,3 +198,6 @@ private:
     static_assert(std::is_trivially_copyable_v<T>, "T must be trivially copyable in a BitField");
 };
 #pragma pack()
+
+template <std::size_t Position, std::size_t Bits, typename T>
+using BitFieldBE = BitField<Position, Bits, T, BETag>;
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index 37f09ce5f..d0284bdf4 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_executable(tests
+    common/bit_field.cpp
     common/param_package.cpp
     common/ring_buffer.cpp
     core/arm/arm_test_common.cpp
diff --git a/src/tests/common/bit_field.cpp b/src/tests/common/bit_field.cpp
new file mode 100644
index 000000000..8ca1889f9
--- /dev/null
+++ b/src/tests/common/bit_field.cpp
@@ -0,0 +1,90 @@
+// Copyright 2019 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <array>
+#include <cstring>
+#include <type_traits>
+#include <catch2/catch.hpp>
+#include "common/bit_field.h"
+
+TEST_CASE("BitField", "[common]") {
+    enum class TestEnum : u32 {
+        A = 0b10111101,
+        B = 0b10101110,
+        C = 0b00001111,
+    };
+
+    union LEBitField {
+        u32_le raw;
+        BitField<0, 6, u32> a;
+        BitField<6, 4, s32> b;
+        BitField<10, 8, TestEnum> c;
+        BitField<18, 14, u32> d;
+    } le_bitfield;
+
+    union BEBitField {
+        u32_be raw;
+        BitFieldBE<0, 6, u32> a;
+        BitFieldBE<6, 4, s32> b;
+        BitFieldBE<10, 8, TestEnum> c;
+        BitFieldBE<18, 14, u32> d;
+    } be_bitfield;
+
+    static_assert(sizeof(LEBitField) == sizeof(u32));
+    static_assert(sizeof(BEBitField) == sizeof(u32));
+    static_assert(std::is_trivially_copyable_v<LEBitField>);
+    static_assert(std::is_trivially_copyable_v<BEBitField>);
+
+    std::array<u8, 4> raw{{
+        0b01101100,
+        0b11110110,
+        0b10111010,
+        0b11101100,
+    }};
+
+    std::memcpy(&le_bitfield, &raw, sizeof(raw));
+    std::memcpy(&be_bitfield, &raw, sizeof(raw));
+
+    // bit fields: 11101100101110'10111101'1001'101100
+    REQUIRE(le_bitfield.raw == 0b11101100'10111010'11110110'01101100);
+    REQUIRE(le_bitfield.a == 0b101100);
+    REQUIRE(le_bitfield.b == -7); // 1001 as two's complement
+    REQUIRE(le_bitfield.c == TestEnum::A);
+    REQUIRE(le_bitfield.d == 0b11101100101110);
+
+    le_bitfield.a.Assign(0b000111);
+    le_bitfield.b.Assign(-1);
+    le_bitfield.c.Assign(TestEnum::C);
+    le_bitfield.d.Assign(0b01010101010101);
+    std::memcpy(&raw, &le_bitfield, sizeof(raw));
+    // bit fields: 01010101010101'00001111'1111'000111
+    REQUIRE(le_bitfield.raw == 0b01010101'01010100'00111111'11000111);
+    REQUIRE(raw == std::array<u8, 4>{{
+                       0b11000111,
+                       0b00111111,
+                       0b01010100,
+                       0b01010101,
+                   }});
+
+    // bit fields: 01101100111101'10101110'1011'101100
+    REQUIRE(be_bitfield.raw == 0b01101100'11110110'10111010'11101100);
+    REQUIRE(be_bitfield.a == 0b101100);
+    REQUIRE(be_bitfield.b == -5); // 1011 as two's complement
+    REQUIRE(be_bitfield.c == TestEnum::B);
+    REQUIRE(be_bitfield.d == 0b01101100111101);
+
+    be_bitfield.a.Assign(0b000111);
+    be_bitfield.b.Assign(-1);
+    be_bitfield.c.Assign(TestEnum::C);
+    be_bitfield.d.Assign(0b01010101010101);
+    std::memcpy(&raw, &be_bitfield, sizeof(raw));
+    // bit fields: 01010101010101'00001111'1111'000111
+    REQUIRE(be_bitfield.raw == 0b01010101'01010100'00111111'11000111);
+    REQUIRE(raw == std::array<u8, 4>{{
+                       0b01010101,
+                       0b01010100,
+                       0b00111111,
+                       0b11000111,
+                   }});
+}