int mulC4(int j, int k){int sum = 0;
   {int x=16; while(x--) if((j>>x)&1)
   {int y=16; while(y--) if((k>>y)&1)
      sum ^= 1<<(x^y);}}
   return sum;}

// Merely a test below
#include <stdio.h>
int main(){int q=1<<16; while(q--) {
   if (mulC4(0, q)) printf("Zharg: %d \n", q);
   if (mulC4(1, q) - q) printf("Zhang: %d \n", q);}
   printf("3*2 = %04x\n", mulC4(3, 2));
   printf("8*5 = %04x\n", mulC4(8, 5));
   return 0;}