tagged_ptr.c

#include <stdio.h>
#include <stdint.h>
#include <assert.h>

static_assert(sizeof(void*) == 8, "Pointer size must be 64 bits!");
static_assert(sizeof(uint64_t) == 8, "uint64_t size must be 64 bits!");

#define _INTERNAL_TPTR_PTR_MASK     0x0000FFFFFFFFFFFFULL
#define _INTERNAL_TPTR_FLAGS_MASK   0xFFFF000000000000ULL

#define TPTR(type) type##__tagged_ptr_
#define DEFINE_TAGGED_PTR(type) typedef uint64_t type##__tagged_ptr_;

#define TPTR_CREATE(type, ptr, flags) (TPTR(type))((uint64_t)(ptr) & _INTERNAL_TPTR_PTR_MASK) | ((uint64_t)(flags) << 48);
#define TPTR_GET_PTR(type, tagged_ptr) ((type*)((tagged_ptr) & _INTERNAL_TPTR_PTR_MASK))
#define TPTR_GET_FLAGS(tagged_ptr) ((uint16_t)(((tagged_ptr) & _INTERNAL_TPTR_FLAGS_MASK) >> 48))
#define TPTR_SET_FLAGS(tagged_ptr, new_flags) (tagged_ptr) = ((tagged_ptr) & _INTERNAL_TPTR_PTR_MASK) | ((uint64_t)(new_flags) << 48);
#define TPTR_GET_DATA(type, tagged_ptr) (*TPTR_GET_PTR(type, tagged_ptr))

// Define Type
DEFINE_TAGGED_PTR(int)

int main() {
    int pointedData = 42;
    uint16_t flags = 0xAABC;

    // Create the tagged pointer
    TPTR(int) tagged_ptr = TPTR_CREATE(int, &pointedData, flags);

    // Print pointer and flags
    printf("PTR         : 0x%p\n", &pointedData);
    printf("TPTR        : 0x%p\n", (void *)tagged_ptr);
    printf("TPTR->PTR   : 0x%p\n", TPTR_GET_PTR(int, tagged_ptr));
    printf("TPTR->Flags : 0x%04X\n", TPTR_GET_FLAGS(tagged_ptr));
    printf("TPTR->Deref : %d\n", TPTR_GET_DATA(int, tagged_ptr));

    // Test Set Flags
    uint16_t new_flags = 0x5A5A;
    TPTR_SET_FLAGS(tagged_ptr, new_flags);
    printf("Flags->TPTR : 0x%p\n", (void *)tagged_ptr);
    printf("TPTR->Flags : 0x%04X\n", TPTR_GET_FLAGS(tagged_ptr));
    
    // Check
    assert(TPTR_GET_PTR(int, tagged_ptr) == &pointedData);
    assert(TPTR_GET_FLAGS(tagged_ptr) == new_flags);
    assert(TPTR_GET_DATA(int, tagged_ptr) == 42);

    return 0;
}