How to combine 4 uint32_t ints into a whole 128 bit int and return

Question

As part of a struct(let's call it ASM) in a header file there are declared four uint32_t ints.

uint32_t Result1; 
uint32_t Result2; 
uint32_t Result3; 
uint32_t Result4; 

I want to access these like this: ASM->Result1, ASM->Result2 etc and combine them into one 128 bit int with Result1 being bits 0-31 from the left, so in the end I'd have:

return 128bitint = Result1Result2Result3Result4;

How can this be done?

Answer 1

I'd use union:

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

int main(void) {
    union {
        struct {
            uint32_t v1;
            uint32_t v2;
            uint32_t v3;
            uint32_t v4;
        } __attribute__((packed));
        unsigned __int128 i128;
    } t128;
    t128.v1 = 0x22221111;
    t128.v2 = 0x44443333;
    t128.v3 = 0x66665555;
    t128.v4 = 0x88887777;

    printf("0x%016"PRIx64"%016"PRIx64"\n", (uint64_t)(t128.i128 >> 64), (uint64_t)t128.i128);

    return 0;
}

This gives:

0x88887777666655554444333322221111

as a result on intel (little-endian) architecture.