Question

When I try to carry out hex multiplication of 16 bits by 16bits using the datatype int64_t, the result displayed is restricted to 32 bits, and a 33rd bit, if present is never displayed, although I am defining the operands as well as result to be 64 bits in length.

Here is the simple code I am using:

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

int main()  
{  
   int64_t a, b, r;  
   a = 0xabcd;  
   b = 0xdbca;  
   r = a * b * 3;  
   printf("%x", r);  
   return 0;  
} 

Result printed out is : ba7fcc46

Expected Result is : 1ba7fcc46

Kindly help me out here.

Answer 1

A popular solution is to use %llx for your printf format. ll means long long (64-bit long on virtually all systems), although this is not portable.

The portable (however, less legible) solution, is to use @anatolyg’s answer, reprinted here:

#include <inttypes.h>
// ...
printf("%" PRIx64 "\n", r);