How do I multiply 2 32-bit integers to produce a 64-bit integer?

Question

How do I take an input of 2 32 bit unsigned integers, multiply them and get the output as a 64 bit integer in C? Any help is appreciated! Thanks.

Answer 1

#include <stdint.h>

uint64_t mul64(uint32_t x, uint32_t y) {
    return (uint64_t)x*(uint64_t)y;
}

Answer 2

Convert the two integers to 64 bit first, then do a normal multiplication and return the value.