I am writing a tool to port games written in C/C++ from the 24bit eZ80 to Windows/Linux. One of the issues is that int24_t doesn’t exist on x86/x64.

typedef uint32_t uint24_t doesn’t always work, especially with packed data and incrementing uint24_t* pointers. I tried _BitInt(24) in Clang C23, but I then found out that sizeof(_BitInt(24)) is 4 bytes, with -Wcast-align stating that the alignment for _BitInt(24) was also 4. I tried _ExtInt(24) but it also had a size of 4 bytes.

So far, I have only found two solutions where int24_t is exactly 3 bytes packed.

typedef struct int24_t {
    uint8_t n[3];
} int24_t;

The first being a struct. But this requires a lot of refactoring in the code, as int x = y + a * b on the eZ80 would become int24_t x = ADD_INT24(y, MUL_INT24(a, b)), which is not as readable.

class int24_t {
    private:
        uint8_t n[3];
};

The other solution I found was to use a C++ class, which is also exactly 3 bytes in Clang and GCC. Since this allows for operator overloading, expressions can be written normally int24_t x = y + a * b. However, since C and C++ are different languages, compiling C as C++ might not always work.

Are there any ways to have a packed int24_t type in C?