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Common/BitUtils: Add operator[] to BitCastPtrType

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This commit is contained in:
Sepalani 2025-08-15 22:26:22 +04:00
commit e9f58193a7
2 changed files with 66 additions and 1 deletions
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15
Source/Core/Common/BitUtils.h
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@ -154,14 +154,27 @@ public:
return result;
}
inline auto operator[](std::size_t index) const
{
using S = std::conditional_t<std::is_const<PtrType>::value, const std::byte, std::byte>;
S* const target = reinterpret_cast<S*>(m_ptr) + index * sizeof(T);
return BitCastPtrType<T, S>{target};
}
private:
PtrType* m_ptr;
};
// Provides an aliasing-safe alternative to reinterpret_cast'ing pointers to structs
// Conversion constructor and operator= provided for a convenient syntax.
// Usage: MyStruct s = BitCastPtr<MyStruct>(some_ptr);
// Usage:
// MyStruct s = BitCastPtr<MyStruct>(some_ptr);
// BitCastPtr<MyStruct>(some_ptr) = s;
//
// Array example:
// BitCastPtr<MyStruct> unaligned_array(unaligned_ptr);
// MyStruct s = unaligned_array[2];
// unaligned_array[2] = s;
template <typename T, typename PtrType>
inline auto BitCastPtr(PtrType* ptr) noexcept -> BitCastPtrType<T, PtrType>
{

52
Source/UnitTests/Common/BitUtilsTest.cpp
View file

@ -3,6 +3,9 @@
#include <gtest/gtest.h>
#include <bit>
#include <vector>
#include "Common/BitUtils.h"
#include "Common/CommonTypes.h"
@ -88,3 +91,52 @@ TEST(BitUtils, IsValidLowMask)
EXPECT_FALSE(Common::IsValidLowMask((u64) ~(0b10000)));
EXPECT_FALSE(Common::IsValidLowMask((u64)(~((u64)(~0b0) >> 1) | 0b1111)));
}
TEST(BitUtils, BitCastPtr)
{
EXPECT_EQ(std::endian::native, std::endian::little);
std::vector<u8> data{0, 1, 0, 2, 0, 3, 0, 0xFF, 0xFF};
u8* buffer = data.data();
EXPECT_EQ(s16(1), Common::BitCastPtr<s16>(buffer + 1));
Common::BitCastPtr<s16>(buffer + 1) = s16(-1);
EXPECT_EQ(u16(0xFFFF), Common::BitCastPtr<u16>(buffer + 1));
EXPECT_EQ(data, std::vector<u8>({0, 0xFF, 0xFF, 2, 0, 3, 0, 0xFF, 0xFF}));
EXPECT_EQ(s32(0xFFFF0003), Common::BitCastPtr<s32>(buffer + 1)[1]);
Common::BitCastPtr<u32>(buffer + 1)[1] = u32(0xFFFFFFFF);
EXPECT_EQ(s32(-1), Common::BitCastPtr<s32>(buffer + 1)[1]);
EXPECT_EQ(data, std::vector<u8>({0, 0xFF, 0xFF, 2, 0, 0xFF, 0xFF, 0xFF, 0xFF}));
#pragma pack(push, 1)
struct MyStruct
{
u16 v16;
u8 v8;
};
#pragma pack(pop)
MyStruct s1 = Common::BitCastPtr<MyStruct>(buffer + 1);
EXPECT_EQ(u16(0xFFFF), s1.v16);
EXPECT_EQ(u8(2), s1.v8);
s1.v16 = 4;
s1.v8 = 5;
Common::BitCastPtr<MyStruct>(buffer + 1) = s1;
EXPECT_EQ(s16(4), Common::BitCastPtr<s16>(buffer + 1));
EXPECT_EQ(s8(5), Common::BitCastPtr<s8>(buffer + 3));
EXPECT_EQ(data, std::vector<u8>({0, 4, 0, 5, 0, 0xFF, 0xFF, 0xFF, 0xFF}));
auto struct_array = Common::BitCastPtr<MyStruct>(buffer + 1);
const MyStruct s1_again = struct_array[0];
EXPECT_EQ(u16(4), s1_again.v16);
EXPECT_EQ(u8(5), s1_again.v8);
MyStruct s2 = struct_array[1];
EXPECT_EQ(u16(0xFF00), s2.v16);
EXPECT_EQ(u8(0xFF), s2.v8);
struct_array[1] = s1_again;
s2 = struct_array[1];
EXPECT_EQ(u16(4), s2.v16);
EXPECT_EQ(u8(5), s2.v8);
EXPECT_EQ(data, std::vector<u8>({0, 4, 0, 5, 4, 0, 5, 0xFF, 0xFF}));
}